Ok.. lets get things straight before we begin... London bridge as a lot of people refer it to is a very boring crossing over the Thames.
Tower Bridge is the ornate one, and this is what it's called!
Opened in the late 19th Century, it is a twin span bridge, with arms that can lift to let boat and sea traffic through if needed.
Its lovely an ornate, and with Tower Hill and The New city hall in the background, makes for a lovely photographic spot.
(The reference "For Fenchuch street and the DLR" comes from when you get off the tube at Tower Hill ... the local commuter service runs from Fenchurch street, connecting it the South Essex link, and the Docklands Light Railway also runs from here too)
Linkies:
Tower Bridge (Wiki)