A trap designed to cause agony and pain to character in the slowest possible form. This trap uses no magic but requires magic to get out of. It is simple yet deadly.
This trap has two parts to it. A weighted 10’x10′ stone block that drops from the ceiling and a pressure plate within a room ahead. The weighted stone slab should reside within a hallway as part of the ceiling leading up to the room with the pressure plate. The slab should be large enough to cover the entire hallway with 10′ in depth. You should make the room large enough to fit the entire party easily. Fill the room with alluring items that would want to make a PC enter within to explore: a chest, a mound of gold coins, or a wizards library. Within the room there is a strategically placed pressure plate at least 30′ from where the slab is located. Upon clicking the plate it will release the hold mechanism on the block causing it to smash down in the hallway covering the entire width and height. Any PCs caught within that area are instantly killed. Any PCs within the room will be trapped with limited air and time. The walls of the room should be of stone so hard it would take the PCs weeks to dig through. Only magic such as Passwall, Rock to Mud, Stone to Flesh, Teleport, or the like would be able to get the PCs out. A lesser spell like Gaseous Form would not work.
Note: Some hints maybe given depending on the situation. A dwarf or someone with mining skill may have a chance to notice the stone of the walls changed or the creases within the balanced slab are not as tight as they should be. A truly malicious DM would place the block in a key intersection of the dungeon far away from the PCs. All they would here is a load stone crash. Unless the PCs explore the thunderous sound limit their air and time within the dungeon. An undead tomb would be a good place as the dead need no food, water, or air to live.