Stonehenge is an archaelogical site in Southern England.
East towards London
Go back on the A303 but better you arrive to Amesbury roundabout where there is a petrol station with restaurants.
The best way to arrive is taking the A303 that passes all around the site. Ask your driver to drop you off at any of the small pull over areas along the road, the traffic doesn't go that fast and they can stop easily, if not there are roundabouts couple of km before and after.
Accommodation and Sleep
The meadows down the ruins are perfect to camp, just mind the cows and sheep! On the upper part of the hill there are also some hippie vans who you can ask hospitality in case you don't have a tent. They have also a petition to make free (legally) the entrance.