The party stumbles upon the entrance to an over grown temple. They are obviously going to be alert to anything out of place.
Just inside the entrance is a metal gate. To one side is a lever, hinged at the floor, that is clearly attached to the gate and appears to be holding it in place. Through the gate the party can see a room about 25 feet in diameter with smooth walls curve inward gradually. Upon further inspection the party may see that the walls have rows of small holes circling the room at different heights.
At the far end of the room is a set of large gears that stack toward the top of the room where a ledge can be found. The trap is not activated by the lever but by the door sliding out of the way. When the door slides into the trigger the floor beneath them quickly rotates straight up dumping the party into the room. When in the room the party begins to hear flowing liquid and the gears begin to turn.
Now that it is obvious it is a trap--this is where I get my stop watch out, start the timer, and say "Go!". I give the party members 3 minutes real time to figure out how to get out and to get there. The way out is obviously up the turning gears. The party members must all roll enough successful checks to make it up to the top. To make it difficult, failed checks drop them back down a gear. The diameter of the gear will determine DC and make this adaptable to any level party.
The Bad Stuff:
At a certain time interval activate the lowest ring of holes. From which comes spurting your choice of two part fire oil that ignites when mixed or some sort of acid that burns. Next time interval ignites the second ring of holes. The party should be out by the time the third ring goes off or take the damage.
If your feeling really mean you can knock them back into the pit of fire when they get hit by the last ring. A smart agile party member will make his way to the top and attempt to throw a rope to the rest. You may allow this or come up with a way to prevent this. I like this trap because it turns the relaxed thought process into a frantic real time, dice rolling, race to the top.
For those that don't like this its only for 3 minutes.