A funny and useless machine that works with TNT and is also survivable in survivalmode.
You stand on the TNT and press the switch. The player falls into a three-block deep hole with water, which closes over the player with a block. The explosion can be seen and heard from outside. Shortly after, the hole opens, with another block underneath. Shortly after, the player probably keeps next door falls out of the ceiling, revealing the mechanism.
The redstone line on the bottom right is the one from the switch, it splits shortly after, one of which ignites the TNT from below, while the other pushes a normal piston aside via the second branch, thus releasing the redstone line next to it. This leads to the piston that causes the hole to close over the player. The piston is pulled back over the shorter delay by again a normal piston blocking the pipe on the other side of the first piston. Meanwhile, the second (outer) delay runs through and does the same thing as before with the first piston, but it sits underneath and is only reset by the player when the player comes (via the ladder from the pool of water and where the TNT ignited) and steps on the pressure plate, causing it to fall back into the room. There are a few more stacks of TNT in the crate next to it.
Annotation: I only found out afterwards that you can save yourself a bit of redstone by coupling the reset of the first piston with the pressure plate on the room, sorry in advance.
Here's the other Redstone fun machine on this site: https://minecraft-bauideen.de/597-Die-nutzlose-Maschine