Bottomless Pit with Scare
I've wanted to create a bottomless pit for >5 years, yet wanted to make it my own. (with a scare) There have been discussion of using pneumatics in combination with a bottomless pit, but since it is an illusion... might as well use the light/dark illusion to give the scare.
Most bottomless pits use 1 half silvered mirror for the top and a real mirror on the bottom. I've used 2 half silvered mirrors in this pit and made a 7" deep secret compartment beneath the bottom mirror to store my skull and strobe light to be triggered 3 sec after a TOT leans over to look into the pit. When the secret compartment is dark, the bottom mirror just reflects. When light is turned on in the bottom compartment, you start to see the skull in it.
Added powered speakers with mp3 player that is turned on at the same time as the strobe should add to the startle effect.