Here is another installment of exTRAPaganza, our Thursday over-the-top trap series.
A huge pit, accessible via a small opening opens up below you. A steel carriage, operated by a mechanical winch, can be lowered into the pit. Below, in the pit, is a vast lake with a small island directly underneath. Gold glitters below.
The winch works fine and takes the party down without effort. As they descend, the PC’s will notice an odd smell in the air. Open flames will begin to ignite pockets of gas about 1/4 of the way down. By the time they are halfway down, the entire cavern will ignite.
There is lots of gold on the bottom, and also a few skeletons in the gold, but the lake is made of flammable liquid. When it is time to return, the winch will be stubborn, and smart PC’s will deduce that it may very well spark (which it will after 10 feet of travel, igniting the entire cavern). The chain is also greased, making it extremely difficult to climb.