Going to London for 5 days then off to France and switzerland ending up back in London and staying near the airport for 2 days.would like to do a full day trip including Windsor. Any ideas?
Why not stay in Windsor? It is about a 15 min. cab ride to the airport. Windsor is a great town to visit. The castle is one of my favorites and its gardens are lovely. There is the Long Walk, a walk over to Eaton, nice shops and some "outlets" for some designers/highstreet shops, too. We have enjoyed a Thames cruise from the bridge over to Eaton- you get to see a different view of the castle and a bit of the countryside. From Windsor you could also take the train (back to Slough first to change) to Bath or Cardiff Wales, I think.
I agree with Toni. Windsor is an easy trip from Heathrow. The castle is great and so is the the town itself. If you are there in the evening, Evensong in St. George's chapel on the castle grounds is really neat to see. Outside this area, you can visit Bath or Cardiff, but that is maybe further away than I would go at the end of a trip before a transatlantic flight, simply my opinion though :).
With a car, you can hit Windsor then Stonehenge and Avebury. The total driving time is about three hours, but the run from Avebury back to Heathrow/Windsor is an hour and a half of it, so it doesn't matter if it's late in the day. Stonehenge takes a bit more than an hour, Avebury, Woodhenge, Silbury Hill, and West Kennett long barrow will take a bit more than three. If you need to shave time, make it just Avebury for an hour and a half. Windsor can take a couple of hours or a couple of days.