I saw a vedio on youtube for a floor-colapsing fortress.
It is a structure with a block of tnt and sand ontop of it. There is wool coming from the TNT so when you light the wool a while later the TNT will explode, sending the sand down.
First Try: Made it out of wood instead of stone. When I lit the fuse the wood around it got lit to, and there were 2 treese beside the structure... There is STILL logs burning.
Second try: MADE IT OUT OF STONE! but the floor was dirt. Big gaping hole where the ground was.
Third try: MADE THE FLOOR OUT OF 3 BLOCK THICK STONE! But I misplaced a TNT block. When I tried to get it back, BOOM
FOURTH TRY: Not Finished yet. This time I hope not to be stupid.