Space Center Houston is an absolute must. We were there for about 6 hours and it wasn't enough time to see everything. Don't miss the Mission Control Center tram tour. The documentary film, "Down to Earth: The Astronaut Perspective," was stunning! I'm going to watch it again on Youtube, but it's really a big screen experience. If we're ever in Houston again, I'll make a return visit with my wife, kids and/or grandkids.