I came back to this place, that was my home for 4 months in 2011.
Just 30 minutes from London, you can visit Windsor. A lovely small town where you can visit the Windsor Castle. The Queen's summer residence.
You can arrive in a commuter train, either from Paddington or Waterloo. Or by bus from Victoria St. I recommend the Paddington train, it might be much cheaper if you are lucky.
In the 1908 olympics games, the marathon race started in Windsor and finished in the White City Stadium. For the first time, the distance was 26 miles, and since that day it has been the official distance.