In many movies about ancient Egypt (most recently perhaps The Mummy and it’s sequels/spinoffs), in National Treasure, in many Clive Cussler caliber adventure books, etc., treasure hunters come across a stone wall that when an ancient key is inserted (an ankh, a carving, etc.) the wall moves away to reveal a hidden room.
Out of curiosity, would there even be a way to conceivably build a room that would do this? What would you use to move the walls?
While I doubt anything like this exists, what are some of the more ingenious actual bits of pre-modern architecture you’ve read about involving architectural secrets?