The picture of the Tower Bridge brings back memories of London. I've really enjoyed both London and Prague. If you are looking for history, both have it, although much of London's was bombed out during WWII. The British Museum is a great visit for a history nerd. (My wife wasn't as impressed with the Egyptian, Assyrian, and other assorted antiquities--of course stolen courtesy of the British Empire, but it was cool to see it under one roof) It's also neat to see Parliament and Big Ben, St. Paul's, and Westminster. In Prague, there's the Old Town Square, the Castle, Bethlehem Chapel, among other things. I've basically had only a day in each city, so I'm sure I missed much of what there is to see. As an American, it's great to see other cultures.