At the Connecticut Science Center, there is a MagLev, or magnetic levitation exhibit on the 4th floor that is one of the best I've seen. It is for older students and adults, requires some reading and some exploration of the adjacent exploratory exhibits in order to fully experience the phenomenon/engineering marvel of propelling trains by magnetic levitation. They have modified the exhibit since the museum opened and they maintain it well. I have been to the museum many times and it is always working, but not always crowded with visitors.
I actually liked the exhibit more when it used magnets of different strengths to demonstrate how that would change the speed of the train, but the weaker magnet strengths sometimes caused the trains to stall and it would confuse some exhibit participants. The resulting exhibit is easier to understand, but less inquiry oriented, and more "my train is faster than your train"!