If, like Willie Green, you are interested in public transit, I recommend visiting two great exhibits on the history of said topic. One is at the National Building Museum in Washington, DC, a place I didn't know existed 6 months ago :-/ (natch, it's at a Metro stop), the other at the headquarters of the Southeastern Pennsylvania Transportation Authority in Center City Philadelphia. They are great exhibits and the book/gift stores aren't bad either. I bought books at both museums.