A high quality 3D movie (with glasses!) of sphere eversion, like this one
Something to help people "visualize" higher dimensions like the video found here
A Let's Make a Deal game show room, where people can play the game to death on a computer until they believe that they should switch doors. Offer candy prizes.
A scaled down Bridges of Koinsberg room, where you can try to walk across each bridge only once.
A large transparent (working!) replica of an Enigma machine.
A Velcro covered life-size Mobius strip which you can walk on with Velcro shoes (I hope you have good insurance)