Leo Hostel ran a tour to the 'Secret Wall', away from the other very touristy sections of the wall. They guaranteed that we would be the only ones there and true to their word we were.
We were driven past the popular section of the wall in Badaling, which was absolutely packed with people in funny hats. About 20 minutes later we ended up getting dropped off in the middle of nowhere, where we hiked for about an hour up to the wall. It was probably the highlight of the trip. both just the wall itself and the fact that we were on our own.
I cna't recommend this trip enough. Book through Leo Hostel, located just southwest of Tiananmen Square.