Traps. They are the bane of many a treasure seeker and explorer of ruins alike. They range from the humble, yet classic, pit trap, to the arcane enchanted one that messes with the nature of time itself, to everything else in between.
They serve multiple purposes from stopping would be thieves from making off with a valuable object to being a source of entertainment for a bored beast.
Whatever the reason, knowing more details about the trap will help you describe it.