If you want to walk part of the ridgeway then park in Avebury main car park and walk down green street up to the ridgeway, turn right and walk to the sanctuary, walk the kennet Ave back to Avebury or go via Silbury & WKLB and stop at the Waggon & Horses for lunch and walk the beckhampton ave back to avebury.
Do Not park at the sanctuary as vehicles are often broken into there.
PeteG