One of our finally areas that we were exploring lead us to a room with a HUGE installation that looked a lot like an adult erector set. It was a cityscape with a complex track for thousands of little cars to zip along. We quickly realized that it was actually motorized and we had come in just in time to have them turn the motors on so we could see all the moving parts.
The piece is Metropolis II by Chris Burden and it was entirely worth the trip to LACMA all on its own!
And to see it in action...some video footage