Box Hill can be found off the main A24 between Leatherhead and Dorking, it is along a dual carriageway with some deceptive bends and a nice little blast down to the roundabout.
The main car park, Rykas and gathering place for bikes is at the bottom of Box Hill and you can enter this from the Burford Bridge roundabout entrance. If you are heading south towards Dorking you can enter directly from the A24 on a short slip road just before the roundabout.