1. Have two pianists learn a fairly difficult piece (by Chopin or whoever) and have one pianist transpose the piece by a half step. Then both pianists would perform the piece simultaneously.
2. Create a film in the style of a silent film, but with voices, sound effects, etc. Give the film to a pianist as a silent film and have the pianist write and perform the score for the movie. Film the pianist playing the score while playing back the sound from the movie. It's a reverse silent movie!!!