The party has been scrounging around in the lower levels of an ancient castle ruin for a couple days. Its moist, cold and they are tired, looking for a way out (or deeper into the depths). A long hallway (or tunnel) about ten feet wide presents itself and they cautiously enter it. The torch light flickers, lighting the way only a short distance ahead. They make their way slowly along the slime covered floor. As they make their way along, the end of the hallway (or tunnel) is nowhere in sight. Unknown to them, they have triggered the hidden trap. They keep walking slowly, cautiously. The hallway keeps going.
After a half hour of walking, the point man notices tracks on the slimy floor. Their senses alerted, the party is even more cautious, unsure what lies ahead. A little while longer, the point man notices that there are even more tracks on the floor but there hasnt been any doorways or entrances along the hall for another group to join the first. Unless they missed a hidden or secret door somewhere. A close examination reveals that the tracks just appeared to join the first set. They arent coming from the side walls from a hidden entrance.
What the heck is going on here…
The Trap is a teleporting hallway, a minimum of 200 feet long. The hall or tunnel is actually a dead end. An illusionary hallway appears at the dead end, making the hall look longer than it actually is. A similar illusion has appeared at the original entrance to the hallway as well, making it, too, look like it goes on. As the party reaches to within 25 to 50 feet of the actual end of the hall, the whole group is teleported back, close to the entrance. They dont feel a thing or notice that the teleport has taken place. Its only after the first teleport that they may notice something along the way that looks odd, like the additional track in the backstory above. It shouldnt be too difficult once they are alerted to something odd that they figure out what has happened. If they try backtracking to exit the hallway, there is a teleport on that end as well sending them back towards the dead end. The only way to exit the hallway is to walk backwards out of the original entrance. Any attempt to exit walking forward will result with the party being teleported to the opposite end of the tunnel. This should keep the GM amused and the party flustered as they try to figure out how to get out of the hallway.