The next time you're in London, you can see Big Ben again. The locals know what's out there. So strike up conversations and ask for suggestions.
Most towns have a tourist office, sometimes several.
Tell them you're looking to leap off the tired old tourist track. Have a game plan even before you leave home. If you have one paramount passion, consider making it the theme of your trip. Visit the favorite hangouts of Jack Kerouac or Isadora Duncan, for instance, or go from maze to maze. Your Cyber Black Book , information when you're away from home.