A natural stone with a hole in the center and gift from the earth to the lucky finder.
A totally throw away .. cannon fodder ..shove it in the mouth of the monster and run for it type of character. Useful though for ‘taken with a pound of salt’ information and running small unsavory errands.
The PCs encounter an elaborate trap room, designed to fill with water, drowning those inside. Clever and resourceful, they disable the trap and move on.
Only later do they discover that this room is part of the elaborate cooling system that prevents beasts of elemental fire from overrunning the complex. While the fiery beasts run rampant, they begin setting fires, which causes the complex to become increasingly hot and smoke-filled. Additionally, the PCs now have to fight their way out past aggressive fire creatures...