Experience Music Project in Seattle is an interactive museum where the visitors not only can see various music related exhibitions, but they can interact with them. They have sound-proof rooms where people can try playing various instruments. For example there is a studio with a drum set and two guitars for people to jam in. Here I am in one of those rooms just playing the drums:
http://vimeo.com/27063396

There is also this drum circle which consists of a touch sensitive surface with a projection of percussion musical instruments. When you tap on the virtual drum, you can hear its sound. There is a background rhythm being played for the visitors to play along with.
http://vimeo.com/27060932

And then there is this massive upside down cone of guitars:
http://vimeo.com/27060862