London would be sweet.
Exploring the houses of parliment, Big bed, the wheel, the Gherkin (Also known as the rocket building, St Mary Axe or the Swiss Re building), the tower of London, tower bridge, Trafalgar Square, the underground, Battersea Power Station and various museums and galleries. It would also be fairly easy to incorporate other European countries because of the channel tunnel and/or a boat (its just over an hour that way to France).
If you go further afield you can start to bring places like Heathrow, Gatwick, Stonehenge, fluff something about moving the HMS Victory so its in London. Xpac's to places like Bristol, Edinburgh or Warwick.
Could be so awesome.