Here is the place I was referring to. It's right outside the Tower Hill tube station. It's HUGE! You really cant miss it!

It has an interesting time line all along the outside of it. It gives info on the city from roman times to present.

The next sundial is outside Tower Hill tube station, and you can get there by tube from Blackfriars. If it is a fine day, (and after it is re-opened sometime in 2002) you could walk over the Millennium footbridge, past the new Tate Modern art gallery, and continue along the south bank riverside walk, making diversions if you like to see the Globe Theatre or Southwark Cathedral.. Ignore Southwark and London Bridges, and cross back to the north bank at Tower Bridge. As you cross the river, the Tower of London will be on your left, and behind it, further away from the river, is Tower Hill station. This has a large horizontal sundial in a small courtyard outside the Tube station.