This encounter was originally themed around a sea adventure on a remote deserted island. The water in the cave and cavern is created from the tides of the ocean, filling the room and covering the floors in around a foot of water, but can be used in any underground campaign setting. Due to the use of cannons, this challenge is designed to be used in an period of time and/or campaign/adventure where black powder or some equivalent is available. The use of this encounter will eventually destroy a lot of the room it takes place in, unless the PCs abort the challenge within the first few rounds, at which point they may come back finding things just as they left it, unless other adventurers tested their fate. It is recommended that one uses this encounter knowing there is no way out beyond a certain point but to move forward.
As mentioned, I've designed this encounter within an adventure that was meant to be a tangent in one of my campaigns. The cave can very well be used anywhere in your campaign. I've adjusted any stats listed to fit 3/3.5e campaigns but have listed the information for 4th Edition... Please let me know if adjustments need to be made. With that understanding, let's begin...
Cannons At The Gate
An RPG encounter by : Peter J. DeJesus
Aka d20rpgamer
"The dark wet tunnel finally comes to an end as you walk into a large cavern. You can hear a slight rustle from above echo about as your splashing foot steps come to a halt*. Stalactite and stalagmite can be seen scattered about, even with the soft glow of your burning torches. The cool moist air wreaks of guano and a slight tinge of death."
The room is entirely dark outside of what the PCs can see based on their natural seeing capabilities and what their torches light up. The cavern is around 100 ft. by 100 ft. with the ceiling reaching as high as 70 feet at it's highest and the lowest point just above the levers on the other side of the room being about 40 feet high. Stalactite and stalagmite are scattered about but pose no immediate threat to PCs unless they are standing within 5 feet of one in the event it falls.
Listen DC 15 only hears the movement and rustling of the bats overhead. It is a small colony that poses no threat to the PCs. Move Silently DC 18 does not startle the bats, although the first CLUNK will startle and will cause the bats to going into a frenzy for 1d4 rounds until they all clear the room via the entrance way. A search of the immediate area will come up with no result.
~~INSERT MAP OF ENCOUNTER ROOM HERE~~
As the PCs enter further into the room, they eventually hit dry ground.* On the opposite side of the room stand a large double door and six switches (see diagram below). The door is sealed and can only be opened using the switches (Knock spells and any other magical devices will have no effect on the doors).
*Adjust to your setting. This encounter has my PCs walking through a cave in about 2 inches of water.
Doors: 3 ft thick stone reinforced with 4 inch wide slabs of iron.
"As you venture across the cavern, you begin to see a large reinforced stone double door. The doors stand about 30 feet high and are about 20 feet wide. The iron reinforcements show their age through the rust on the bars. Standing before the doors are six four foot tall metal levers, all showing similar age."
If the PCs approach the door (or Spot DC 15 while standing by the switches), they notice a small inscription carved into one of the doors.
"A push sets the keys,
With a twist to the right.
But one must be forewarned,
For metal will take flight."
This is a clue for the PCs on how to set the levers. The switches are set as follows:
~~Insert Default Lever Diagram~~
"After closer examination of the levers you see the following letters engraved in the floor:
N C B A O B
Each lever, lined up with a certain letter."
At this point, present the diagram of the levers above to your players.
The key to opening the doors is spelling the word CANNON by moving each lever to the proper position and then activating the key by pushing the lever down and twisting it to the right as the poem dictates. The solution is as follows:
~~ Insert Solution Diagram ~~
The Cannons
Five cannons are hidden in little caves that range from 20 to 40 feet above the floor. There are about a dozen little caves but only five contain cannons as depicted in the map above. A Spot DC 25 sees the dark caves in the rock above. The cannons are set back far enough that the PCs can not spot them from any vantage point on the floor. The walls are too moist and steep to climb without assistance. In the event the PCs do manage to get up to one of the caves, ie magical item, flight, or a cunning use of materials in dungeon prior to this encounter (see DM Guide or DM Screen for Climb stats and Difficulty Class based on description), read the following text.**
Mini Caves
"As you enter this small dark cave, a shimmer of light reflects off of a large black metal object. A thin layer of moisture lines the entire room, including it's walls, 3 large metal balls on the floor by your feet, two small barrels, a long rod and the black, slightly corroded metal tube that occupies most of this small space."
**DMs may run a quick scare with any remaining bats that may have not exited these caves.
The tube is one of the cannons. The cannon is loaded and ready to fire. It's about 10 feet long with a foot wide opening on the front end which faces into the cave, aimed at the opposite wall of the cavern. As Search DC 18 reveals it is hooked up to some sort of "complicated looking mechanism". Stress "complicated" A Search 22 sees a ball similar to the ones on the floor deep within the tube but out of arms reach. Disable Device DC 40 successfully disables the mechanism. A fail of 10 or more results in setting off the cannon.*** See Cannons Going Off below.
The two barrels contain the remains of black powder (Alchemy DC 12). It's enough to fit into a small sash for future use but not enough to do any harm. PCs not handling it with care while fire is present face the powder igniting in a flash causing temporary blindness for 1 minute.
The cannons weigh 2 tons each.
***PCs who set off a cannon suffer from Deafness for 2d10 rounds (Ref DC 20 halves time duration)
Dealing with the levers
Positioning the levers into the correct positions to spell out "CANNON" is the solution and key to opening the door way.
The activation of the levers require three actions.
1. Moving the lever to a select letter
2. Pushing down on the lever
3. Twisting the lever to lock it in place
Activation of the first lever (any lever placed in the correct position) activates the mechanism that fires off the cannons.
"A loud grinding of gears is heard beneath the floor below and in the walls around you. It echos in the cavern. The churning comes to a halt with a loud CLUNK"
The mechanism is now active and all the cannons are armed (if not already set off by PCs exploring the upper caves. At this point, players are required to activate all five remaining switches in order to open the large stone double doors leading to the next part of their adventure. Each successful movement and selection of the levers that is made triggers the cannons in sequential order. No order needs to be maintained in lever selection. The cannons and the mechanism running them are designed to fire in a predesigned order***. See Cannons Going Off below for targets and effects of each cannon and it's blasts.
***DMs may adjust and set a cannon to each lever but to keep things simple, I designed it so each cannon sets off in numerical order. Players may enter this encounter to find one or more levers already activated and the effects listed below from it's corresponding cannon littering the floor of the room. One or two blasts were enough to scare off the previous adventure party.
Cannons Going Off
"Rockslide" (Insert Link to Rockslide Video)
3rd/3.5 Edition CR 1
Effected Area: 15 ft radius of burst (Terrain)
Damage: 2d6+6 if caught in effected area
Successful Reflex (DC 19) halves
Effect: Area of the burst becomes difficult terrain w/ 50% chance of fall continuing on next round and spreading and doubling the effected area. 3 round max
4th Edition Level 1 hazard
Terrain XP 100
Recharge: (d6 roll) 4, 5, 6
Attack +4 vs Ref
Detect Nature or Dungeoneering DC 19
Initiative: +3
Immune: Attacks
Attack: Close burst 3 (creatures in burst); +4 vs. Reflex
Hit: 2d6+6 damage
Miss: Half Damage
Effect: The area of the burst becomes difficult terrain
Special: As soon as the attack fails to recharge, the rockslide is over and does not attack again.
If a PC investigates the caves and sets off a cannon, determine which cannon it is on the map and determine it's Effect as listed below.
Cannon 1 : First to fire (unless PCs activate another with failed Disable Device throws as mentioned in Mini Caves above). This cannon is aimed slightly above the main entrance to the right. When activated a loud boom is heard from above. The cannon ball flies across the room and slams into the wall above the right side of the entrance causing a "Rockslide" (details above) under the point of impact, in turn blocking off half the entrance.
Cannon 2 : Second in order to fire (unless PCs activate). This cannon is aimed slightly above the main entrance to the left. When activated, a loud boom followed by the cannon ball colliding with the wall above the entrance creating another "Rockslide" under the point of impact, in turn blocking off the other half of the entrance.
This is the last point in which PCs have a chance to dig themselves out through the rubble and retire to the safety of the passageway out.
Cannon 3 : This cannon is located near the front entrance and is aimed at the upper right side of the double stone door. It's impact creates a "Rockslide" near to the front right side of the door. It's shock wave rattles the weakened stones around it and causes a large slab of the wall above the entrance way to come crashing to the ground. Any PCs caught under this slab are dealt 12d12 damage. Reflex DC 15 halves and they are pinned and bleeding out. Any PC with a successful Reflex save and Evasion escape narrowly with their life.
Cannon 4 : Fourth to fire, this cannon is aimed to the top left side of the double stone doors, also creating a "Rockslide" upon impact next to the large double stone doorway
Cannon 5 : Located directly opposite the double stone door, it is fifth to fire. Due to a large rock formation that obstructs it's aim, this cannon ball does not reach the target above the double stone door, but it does hit the rock formation directly above the levers causing the formation to explode on impact and rubble to fall down on PCs. Handle any in effected area below formation as if caught in a "Rockslide".
"As the dust and rock settle another large CLUNK is heard and echos through the cavern. Gears grinding behind the walls rattle the room as a loud HISSSSSS is heard. The door ahead begins to open outwardly as a gust of _____ air rushes into the cavern."
Adjust to fit the next part of your adventure.
Any assistance in giving this encounter alone an EL or CR would be greatly appreciated. I have yet to try this on my PCs yet but plan to do so in due time. Stats based on "D&D Essentials - Dungeon Master Guide" with my own 3rd Edition conversion. Any assistance readjusting stats if I'm off would be noted and credited below.
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