Here's The Tenager's list, not in any particular order, of Cool Things to Do in London.
Walkin' and Discoverin' stuff
Street Performers - Trafalgar Square
Double decker buses and the Tube
Changing of the Guard
We also went to loads of museums, galleries etc - none made it onto the list!
We didn't go to the Tower of London, Greenwich or any of the markets, so this list is by no means complete...