Activity: Borough Market. Tube Stop: Southwark Cost: Free (except food!) Hours: 10-5, closed Sun.
Ok that was a lot of history. Time to break it up with some markets! Head for Borough Market. There has been a market at this exact spot since 1014. It's beautiful and about an 18 minute walk from Tower Bridge.
After you've finished up at Borough Market, if you are a giant HP nerd like me you can detour to Leadenhall Market where they filmed Diagon Alley (Tube stop: Fenchurch Street). Find the blue optician's store on the corner. That was the entrance to The Leaky Cauldron!
Most of the HP stops are kind of like this. It's in the movie and it's fun to see for big fans, but there's no monument to Harry Potter or anything. I've included only the spots I have personally visited and found magical. If you want to see real Harry Potter stuff, best to make the trip to HP Studios.