Here is an installment of exTRAPaganza, our Thursday over-the-top trap series.
The party enters a large, circular chamber. In the middle of the chamber is a large funnel that appears to descend to nothingness. The sides are glass-smooth.
When the party falls into the funnel (and they *will* fall in to the funnel – use an earthquake, tripwires, exploding floor tiles, falling ceiling tiles, ogres, whatever to get them in there), they immediately begin to slide down. However, instead of taking a direct path, they take a circular path, much like the drop the penny into the spiral wishing well. Stopping the descent and climbing out is physically very hard to do, and would be near impossible without magic or outside assistance. The characters probably won’t worry too much at this point, however, as they can see that once they go down about 20 feet, the opening becomes too narrow for them to pass.
Once they get about 15′ down, however, characters begin to shrink in size so they will fit into the opening. As the opening gets smaller and smaller, the characters keep shrinking. At this point, they are moving quite fast. Outside help such as ropes and such will be very difficult to use, due to the characters’ size. Spell casting with somatic components will also be quite difficult, adjustments to casting difficulty need to be made.
After about 10 rounds, the characters will be too small to be seen from the room. However, the characters will keep slowly shrinking as the funnel slowly shrinks. This effect should last for about 1,000 years, when they finally hit the bottom, which is full of super-tiny, microscopic spikes, and super-tiny, microscopic humanoid remains, impaled on super-tiny spikes.
Of course, any spells that return the characters to normal size after the fifth round will instantly kill the characters, as they will no longer fit in the space provided.