Friday Encounter: Ogres' Ferry

Following up with the theme I've been on for the last few Friday Encounter posts, here's a simple puzzle I used in a recent session. I used it as a room in a dungeon, but it could easily be used in the wilderness as well.

The PCs should come across a river that is flowing too quickly to easily cross on foot, and no bridge or ford in sight. A small rowboat, big enough to hold two people at a time, is sitting on the shore closest to the PCs. Also on the shore with the PCs are a number of ogres equal to that of the party members, who are standing around grumbling and arguing with one another. At the sight of the PCs, they accost them, insisting they need their help to ferry them across the river. They note that they have been stranded here a while, and are growing hungry.

This encounter is based on an old logic puzzle known as the "missionaries and cannibals problem" or "jealous husbands problem" - to boil it down to the essentials, you have to get two parties of equal size across the river, making sure that Party A does not outnumber Party B on either bank of the river at any time.

In this case, the party must transport each ogre to the other side of the river. The boat can hold two people at any time - they can be ogres, PCs, or any combination of the two. However, the ogres are hungry enough to make a bid for the PCs if they think they can get away with it. The ogres are cowards, and they won't try to attack the PCs if there are more PCs present on their bank than ogres. But as soon as they outnumber the PCs on a given bank, they'll attack, ganging up on the PCs so they can kill and eat them.

To make sure this information is available to the players, you may wish to have one of the ogres grab for the outnumbered PC(s) as soon as the boat begins to leave the shore, so that whoever is rowing has a chance to intervene - if the ogres see them change course, they'll immediately drop what they're doing. In any case, the party will either have to take multiple trips to get all ogres and PCs on the other side of the river, or prepare for a fight.

According to Wikipedia, the missionaries and cannibals problem can be solved in a minimum of 11 moves if there are three missionaries and three cannibals (or husbands and wives, brothers and sisters, masters and valets...you get the idea). In order to add urgency to this encounter, you could have the tides slightly rise after each move - the PCs must solve the puzzle in, say, 20-30 moves (to give them leeway to make mistakes) before the tides become too high to safely cross the river. If this happens, they might be swept away, potentially requiring them to make some rolls to avoid being tossed overboard, or perhaps they'd be washed away to a new location. In my campaign, I had three party members and three ogres. If you have a larger party, you'll need to increase the number of alloted moves.

In my campaign, one of the ogres had a broken arm, preventing him from rowing the boat. This would explain why the ogres couldn't row themselves across, and forces the PCs to man the boat at least once. However, my players used this to surmise that the ogre with the broken arm wouldn't be able to fight them either, and that he wouldn't count toward the number of ogres outnumbering the party since he couldn't pose a threat. This made the puzzle significantly easier, but it was logic I couldn't argue with, so I let them have it.

Since I was using this puzzle in a dungeon, I had a door open once all the PCs and ogres were on the same side of the river. You could have this be operated by a pressure plate that will only open under the combined weight of all PCs and ogres standing on it (note that creatures would not need to be alive in order to meet the required weight). Or you could have a passage or treasure located on a higher ledge that the PCs can only access by climbing on the ogres' shoulders.

Friday Encounter: Stepwell Passage

Following on from my last Friday Encounter, here's another dungeon puzzle I've used in a recent session.

This encounter is designed to be used as a dungeon room. The room is dominated by a large stepwell - a pit dug into the ground, with a series of staircases leading downward along its sides to allow groundwater to be carried up. The twelth step from the bottom is covered in gold leaf, while the rest are bare stone. The pit is lined with multiple levels of archways stacked on top of each other, allowing water to be retrieved from different points. Each archway contains a door - some are closed, and some are open to chutes leading either up or down to control the flow of water. The doors have no handle, knob, or mechanism and cannot be opened manually. Furthermore, at the very bottom of the stepwell is a door inset in a golden frame.  Also in the room, there are four pillars in a line leading toward the stepwell, each of which has a wheel set into it.

When the PCs first discover the stepwell, the water is sitting at the level of the third step from the bottom. By turning the wheels attached to the pillars, they can open certain doors on the walls and allow water to flow in or out of the pit, thus raising or lowering the water level. The objective is to raise the water level to the gilded step.

Essentially, this is a simple math puzzle - each wheel raises or lowers the water level by a certain amount of steps. The wheels must be turned completely in order to work, so you can't get a partial effect. You can't have a "negative" water level - if you were to drain more steps than are present in the stepwell, the whole stepwell drains.

You can adjust the values as needed (perhaps even using more or less than four pillars if you want), but here's what I did in my game.

• Pillar 1 (furthest from the stepwell) lowers the water level by 8 steps.
• Pillar 2 raises the water level by 5 steps.
• Pillar 3 raises the water level by 10 steps.
• Pillar 4 (closest to the stepwell) lowers the water level by 3 steps.

So, if the water level starts at Step 3 and the goal is to get it to Step 12, the puzzle can be solved by draining the stepwell by turning the wheels on Pillar 1 or 4, then using the wheel on Pillar 3 to raise it to Step 10, then Pillar 2 to raise it to Step 15, then Pillar 4 to lower it to Step 12. You get the idea.

Once the water level hits Step 12, a gong sounds, and all water flushes out of the stepwell. The gold-rimmed door at the very bottom then opens. In my campaign, this door led to the next area of the dungeon, but you could have it contain treasure or a magic item or the like.

Friday Encounter: Chamber of Tremors

Here's a fairly simple dungeon puzzle I used to great effect at my last session. It's based on Zhang Heng's Han Dynasty-era seismoscope, which was used to detect the direction of approaching earthquakes. Growing up, I had a book on the ancient world with a diagram of the device, which astounded me then and stuck with me well into my adulthood - so it only seemed fitting it would one day find its way into my games.

For this encounter, there should be a large central room in a dungeon dominated by a strange sculpture - a four-sided pillar, with a dragon sculpted on each side, facing each cardinal direction. Each dragon carries a pearl in its mouth, and positioned directly below it is a frog with a wide open mouth, looking up. Close inspection will reveal that the pearls in the dragons' mouths are a separate piece, but cannot easily be removed by hand. There should also be four doors on the walls, leading in each of the cardinal directions.

In each of the rooms surrounding the central room, there should be some sort of interactive element that can generate a tremor. Examples might include striking a gong, dropping iron weights from a ledge, animating a heavy statue, or getting an ogre to strike the floor with its club. I'll leave the exact details up to you, in case you have other ideas - the important part is that the ground should shake on successful completion of each room's task. If the PCs find a way to create a tremor through means other than the intended solution, such as a thunderwave or similar spell, this should also count as a successful completion of the puzzle. The physics at play here is what's important, not the finer details.

When a tremor goes off in each room, it is felt by the mechanisms in the central room. Each dragon is attached to a lever connecting to a pendulum inside the pillar. When the ground shakes, the pendulum is shifted in the direction of the vibration, causing the corresponding dragon's mouth to open and the pearl to drop into the mouth of the frog below.

If the PCs remove the pearl from the frog's mouth, they will hear a clicking noise, indicating that a pressure plate inside the frog has been relieved. The pearls contain no special attributes. If they are placed back in the dragons' mouths, the mouths close and another vibration must be produced in that direction to release the pearl again.

Once all four pearls have been dropped in the mouths of the frogs, the dragons' and frogs' eyes begin to glow blue. If the party stands by the pillar when it is in this activated state, it lifts off the ground, serving as an elevator to take them to a previously inaccessible location in the dungeon.

Friday Encounter: Archimedes's Well

Here's a simple two-room puzzle designed to be slotted into a larger dungeon. This one is based on Archimedes's principle that an object displaces water equal to its mass, and attempts to simplify these physics for the sake of gameplay. Keep in mind that the intended solution to this puzzle may not be obvious unless your players are familiar with the theorem, although there are alternative solutions as well.

There should be one room in the dungeon with a large well in the center of the floor. The well drops a distance of about 200 feet before coming to standing water. Looking into the well reveals that a golden crown is floating atop the water, its surface reflecting light off any torches or lanterns, but it's far too deep to be reached from the surface.

A short distance away from the well is a pile of stones of various sizes. The third feature of the room is a door leading to the north (or whatever direction you want, it isn't important). On the wall opposite the door is a chipped, faded mural of a naked man holding his fists high in triumph, with the word "EUREKA" written over his head.

The intended solution to this puzzle is for the PCs to drop stones into the well, displacing enough water to lift the crown up to where it can be reached. They need to raise the water level a total of 200 feet in order to retrieve the crown.

However, they must do this without making too much noise, or they risk alerting an ogre who resides in the room to the north. When the PCs first enter the room, the ogre is asleep, and the sound of his snoring can be heard if one listens at the door. He's sleeping too soundly to be woken by normal conversation or footsteps. However, if the party makes any loud noises, or isn't careful in how they drop the stones, he will wake up and charge into the room.

If the PCs drop stones into the well, the water level rises by an amount of feet equal to the weight of the stone. They can use any combination of the stones to raise the crown, but every time they drop one, they must make a Stealth check; the ogre is alerted if the check fails.

The pile contains:

• Five 20-pound stones (DC 25; requires two hands to carry)
• Eight 15-pound stones (DC 20; requires two hands to carry)
• Ten 10-pound stones (DC 15)
• Fifteen 5-pound stones (DC 10)
• Twenty 1-pound stones (DC 5)

If the PCs wish to appraise the crown, a DC 15 Nature check will reveal that it appears to be worth 1000 GP. However, if the check passes by a value of 25 or more, it will be determined that the gold of the crown is actually mixed with silver, cutting the value down to 500 GP. Alternatively, you could use the crown for another puzzle elsewhere in the dungeon, such as putting it on the head of a statue to open a door.

Many players might attempt to solve this puzzle through alternative means, such as levitating into the well or using spider climb to scale the walls. Use your judgment to determine how this should be addressed - you should reward PCs for thinking outside the box, not punish them for not guessing what you wanted them to do.

Optionally, if you're worried about PCs getting into the well, you can have a water weird at the bottom, lurking in the water. It lays dormant as long as the PCs stay out of the well, but will come to life and attack if they enter it.

Friday Encounter: Rickety Bridge

Here's a simple environmental puzzle that forces players to rethink how they manage their inventory and how they approach obstacles with limited resources at their disposal. It could be used either in a dungeon, on the road, or in a wilderness environment.

The party will find their path is suddenly blocked by a deep chasm, with steep cliffs plunging 200 feet below. The only direct route across is via a rickety rope bridge - and it is obvious that it will not be able to accommodate a great weight. The PCs will likely have to leave heavier gear behind in order to get across.

It is best to tell the players the mechanics of this encounter so that they can make informed decisions about how they want to approach it. The bridge cannot bear weight greater than 300 pounds; if a load of 300 pounds or more crosses the bridge, it will automatically collapse, sending any creatures on the bridge plunging into the abyss. Furthermore, creatures bearing a load greater than 200 pounds will need to tread carefully in order to avoid putting undue stress on the ropes. For a creature bearing a load of 200 pounds to cross the bridge, they must make a DC 10 Dexterity check, or the bridge will break under their feet. For every additional 10 pounds they carry, increase the DC by 2. A creature bearing less than 200 pounds can cross the bridge without issue.

A "load" here should include the creature's weight and the weight of any equipment it is carrying or wearing - if you don't know exactly how much your character weighs, assume 150 pounds for a medium-sized creature, 75 pounds for a small-sized creature, 100 pounds for a dwarf, and 175 pounds for a goliath. A creature of large size or greater will automatically cause the bridge to break; a creature of tiny size or smaller can cross the bridge without incident.

There are a few ideas at play here. In order to make progress across the chasm, the PCs will likely have to abandon equipment, including heavy armor, treasure, and other useful things, as well as any horses or beasts of burden they may be traveling with. Whatever is on the other side, they'll have to deal with it without such assets. In a hostile environment, there may not be a guarantee that their equipment will still be where they left it if they return to the other side of the bridge to reclaim it, and the presence of such items piled up on the ground may tip enemies off to the PCs' presence nearby. Even if the PCs feel the risk of crossing the chasm is too great, such an obstacle can encourage them to seek out alternative routes, which might cause them to focus their exploration elsewhere. And if the bridge does break, now the remaining PCs will likely have to find another way around anyway!

By default, a fall from the bridge will almost certainly kill most PCs, unless they have access to feather fall or similar effects. However, you could also shorten the drop and have another area to explore below the bridge (or, conversely, change the fall to a drop into a spiked pit). Another option would be to replace the chasm with a rushing river, which could carry PCs - or their gear, if they attempt to ferry it across - downstream.

Friday Encounter: The Hall of Winds

This isn't just your regularly scheduled Friday Encounter - this is also an entry in the Late Summer Blog Competition over at Monsters and Manuals. In the RPG community, noisms might well be one of my biggest influences. I fondly remember following his thread on rpg.net, back when rpg.net was cool, going through the entire 2e Monstrous Manual and discussing the potential worldbuilding implications for every single entry, and when he started his blog, it was one of the first OSR blogs I ever discovered. I've been following his work ever since. Needless to say, I'm a big fan of his - his terrible opinions on cloakers aside - and when he announced the competition, I was just as intrigued as he was by an interesting mosaic he found on a vacation. The thoughts kept flowing from there, and they turned into the next Friday Encounter!

The Hall of Winds

Due to the spatial implications of this encounter, it is best suited for a dungeon. The dungeon can be as big or as complex as you like, but there should be a few features you want to make sure you include. There should be a room somewhere in the dungeon where a series of hallways lead off in each of the eight cardinal directions, and each of those hallways should terminate in a room where a large brazen lion's head with gaping jaws is mounted on the wall opposite the entrance. Additionally, there should be another room elsewhere in the dungeon where a large circular mosaic is set into the floor. The mosaic depicts a compass rose in the shape of a sun, with the image of a sailing ship in the center, and on the wall behind it is another lion's head.

The section of floor the mosaic is on rotates and can be pushed - doing so causes it to turn slowly with a loud sound of stone grinding against stone that can be heard from any adjacent room. When the mosaic is lined up so that one of the points of the compass rose points toward the lion head on the wall, a strong gust of wind billows from out of the mouth of the lion head at the end of the hallway corresponding to that direction. The gust of wind is daunting and unstoppable, and can be felt all the way to the nexus of the eight hallways. It cannot be walked against easily. Any ranged attack made perpendicular to the direction of the wind is made with Disadvantage, and any ranged attack made against the direction of the wind will be turned backward toward the creature that made the attack instead of its intended target. The wind only stops if the mosaic is turned again.

This is a feature with plenty of open-ended applications. The wind could put out torches or other fires. It could spread a fire into another room. It could be used to guide an arrow across a chasm to a target on the other end that would ordinarily be out of reach. It could be used to blow an enemy into a pit. It could uncover a secret passage placed behind a tapestry. I'm sure you can think of plenty of ways this effect could be exploited, and I encourage you to think about how you can incorporate it into how you design dungeons and puzzles. I'm sure your players can think of plenty of ways to exploit it, too; don't be afraid to reward thinking outside the box!

Friday Encounter: The Blazing Pillars

Elder Scrolls Online

Here's a simple puzzle, designed to encourage creative thinking by players, that you can throw in as a random encounter or in a dungeon room. There isn't intended to be any one solution - it's meant to be addressed by thinking in terms of what's possible within the narrative context of the session. Your players may surprise you!

The party should come upon a circle of tall stone pillars - these may be a monument out in the wilderness, or placed in a dungeon room. If outdoors, they should be on a tall hill with little surrounding foliage or rocks to protect the hilltop from the wind. If in a dungeon, the pillars should be in a wide, tall-ceilinged chamber, preferably with cavernous exits to all sides to ensure a draft can pass through easily.

There are four pillars, ranging from ten to twenty feet high; each is five feet higher than the last if one walks in a clockwise circle starting from the shortest pillar. In the center of the circle is a stone platform, fifty feet across, carved with a clockwise spiral. A DC 10 Investigation check will reveal that there is a circular seam in the middle of the spiral, forming a smaller concentric circle fifteen feet across.

Atop each pillar is a shallow bronze brazier, heaped with coals, but these coals are cold and extinguished (they are cool to the touch, indicating they have not been lit in some time). Optionally, the bases of the pillars (at eye level to the PCs) may be carved with designs recalling rising flames and swirling winds, or an image of the four braziers lit simultaneously, if you feel a hint is necessary.

The goal of this puzzle is to light the brazier atop each pillar in sequence, starting from the shortest pillar, moving clockwise, and ending at the tallest, without any of the braziers going out. This is perhaps easier said than done, as the breeze blowing through the circle can easily to extinguish the flames. If one brazier goes out before all are lit, the sequence must be started over from the shortest pillar.

In order to solve the puzzle, the PCs must find a way to light each brazier without the wind blowing them out. They could climb the pillars, but doing so would take time, and the fires might go out in the meantime. They could try to jump from one pillar to the next, but that would create a breeze that could put the fires out. They could use magic or flaming arrows to try and light the braziers from below, but the wind might make aiming difficult. They could try to block the wind, but that might be a daunting task, especially if the circle is outdoors! Just go by what solutions and consequences make logical sense, and use your judgment.

Once all the braziers are lit in the correct order, the smaller circle on the platform recedes into the stone with a rumbling noise, revealing a spiral staircase down into a secret chamber. In this chamber, on a stone slab, is laid a pair of enchanted velvet gloves, their surface embroidered with the images of flames. The gloves are magically resistant to fire; although they feel no different than ordinary gloves while worn, they cannot catch fire by any means, and the hand beneath them will not feel the fire's heat. The rest of the wearer's body remains vulnerable as normal. If this encounter is used in a dungeon, it might be fun to hide treasures or secrets in the same dungeon within fires so that the gloves unlock new options for the wearer.

Alternatively, the DM may wish to substitute another treasure, a clue to an ongoing quest, or a secret passage. Feel free to use whatever would be most useful to your purposes here.