The Endless Dungeon
This is an adventure for a third level character party, but it will work up to fifth-sixth level, and possibly at second level.
As your character party is exploring in the wilderness, they come across a doorway. It is a grand and imposing door, set into a cliff-face, or the side of a hill. It practically begs to be entered and explored, in has the feeling of an ancient temple or tomb, packed to the brim with treasure, even though there are no obvious markings or writings anywhere on the door.
This is exactly the impression the builders intended to convey, they have built a trap for unwary adventurers, to protect their better hidden, true temples, that are further into the hills. As the DM, you will need to decide who these temple builders were, it is left blank so you can simply fit this adventure into your ongoing campaign, using existing adversaries.
The builders created a simple trap, consisting of a stairway leading down into a series of rooms. There are four rooms, each linked by a corridor, that forms a loop. As the adventurers pass into each room, the exit is hidden by an illusion, and they are attacked by a summoned elemental. Each room is dedicated to one of the four elements. As the PCs move around the corridors, they will probably come across the bodies of adventurers who entered the tunnels before they arrived. The bodies of slain adventurers are hidden in the tunnels by the elementals, and are deposited in view as new elemental attacks are triggered, from hidden panels in the walls. This is designed to increase the level of fear in the adventurers, as bodies appear from nowhere as they move around the circle.
Each time they make a circuit of the tunnels, the summoned elementals become stronger, and harder to defeat. The builders of this trap have left a way out for the characters, as is detailed below.
The Doorway, stairwell and first room (Fire)
As the PCs investigate the doorway, they will discover that it is simple to open. Well balanced and well built, it swings open at the gentlest of touches. The door leads on to a well made, dry, stone stairway, that leads down into the hill.
As they descend the stairway, they see a well lit room at the bottom, obviously lit by a number of magical torches. Once the final character enters the room, the stairway is immediately obscured by a Mirage Arcana spell, that creates an illusion of an unbroken wall. This spell is case with a caster level of the party level plus 2.
The room is 25 feet square, and the air is noticeably warmer than would be expected. There are torches placed in sconces at 5 foot intervals around the walls. The entrance was in the middle of the south wall of the room. There is an obvious exit in the centre of the left hand wall, which leads into an upwards sloping corridor.
The corridor and second room (Water)
The corridor is fifty feet long, and slopes upwards with a 1 in 10 gradient. It is 5 feet wide. As the characters move along the corridor, they will notice it getting cooler, and probably see the water that drips from the walls.
At the end of the corridor is a second room, the same size as the first. It is wet and dank. When the first character enters, they are attacked by a small water elemental. Once the final character enters the room, the entrance is again blocked by a Mirage Arcana spell.
There is an exit in the north wall of the room, which again leads to an upward sloping corridor.
The second corridor and the third room (Earth)
As the party move along this corridor, the tunnel dries out, and the wall become crumbly, unfinished earth. In this corridor, there is a 50% chance of finding an adventurer's corpse, as described in the treasure section.
At the end of the corridor it a third room, the same size as the first two. The first character through the entrance is attacked by a small Earth elemental, and once the last character enters, the door is again blocked. There is an entrance to the east, leading to a downward sloping corridor.
The final room (Air), and getting back to the start
Proceeding along this corridor, the party will notice it becoming exceedingly draughty. Again, there is a 50% chance of finding a corpse in this tunnel.
On entering the room at the end of the tunnel, they are attacked by a small Air elemental, and the way back is blocked once more. There is an exit to the south, leading to a downwards sloping corridor (50% chance of discovering a corpse) that terminates in the starting room.
There are no surprises when the party enters the starting room. They are attacked by a small elemental, and the way the entered in once more blocked.
Making another circuit
Each time the party move around the circle of four rooms, their way is blocked as before, and they are attacked by increasing large elementals.
Leaving the Dungeon
It is difficult to leave the dungeon alive. The party can either find a way through the illusions, or they must exit the dungeon the only way the builders allowed, by begging to be allowed to leave whilst in the first room, and swearing to never enter a temple belonging to the builders of this trap. If the PCs agree to this method of exit, they are placed under a Geas to never enter a temple created by the builders, and if they attempt to enter one, they will suffer the ill effects of the Geas spell. This Geas is cast at the level of the character party +2, to a minimum of 6.
On the third entrance to the starting room, flaming words appear in the wall, which tell the PCs about this method of exit.
Treasure in this dungeon comes from the corpses of previous unlucky adventurers who were caught in the trap. Generate suitable equipment for several adventurers at 1st, 3rd, 5th and 7th levels. As the character party make circuits of the temple, the bodies appear in the corridors as described.
When the party enters a room that leads to a corridor that might contain a body, then the summoned elemental in the next room on takes the body from a store of corpses in the ceiling of it's room, and places it in the corridor.
E.g. When the party enters the Earth room, determine if a body is placed in the next corridor. If it is, then the body is removed from a store in the Air room, and placed in the adjoining corridor by the Air elemental.
These stashes of bodies are concealed by Mirage Arcana spells, and if the character party break the illusions elsewhere, they may discover a stash. If they do, then they can collect loot from all the remaining bodies in the stash, which will be bodies that are generated and of higher level than those currently being placed.
E.g. If a stash of bodies is discovered during the second circuit of the tomb, it will contain the gear of one 5th level and one 7th level adventurer.