London's City Hall is interesting to say the least. It's right on the Thames across from the Tower of London. Here's the wikipedia article and here's their web site. Here's a BBC page that has a panoramic view of City Hall. It loads real slow but it's worth it. Just let it pan around and you'll see the Tower across the Thames and Tower Bridge.
This is my photo of City Hall. Notice the black helicopter flying above it. I never did figure out what it was up to.