Piggledene (National Trust) just outside Avebury on the Road to Marlborough. Not so much a quarry but a valley of sarsen erratics from where it's been suggested some of the sarsens now standing at Avebury (and perhaps Stonehenge) were 'harvested'. Among the last harvesting of sarsens from Piggledene were those taken for sleepers for the Swindon tram lines.

Whatever, the little Valley of Dreams (also known as the Grey Wethers because the sarsens look like sheep lying down) is well worth a visit (and a great place for a picnic :-)