It's worth the trip John (regardless of my comment) - I have been many times. Not too far from Swindon and about as different from Swindon as you can imagine, in a very good way I might add. Bev is right, in that you can stroll amongst the stones pretty well freely, across the top of the circular enbankment. A good 'Sunday' place to visit and may I suggest a leisurely stroll on the Ridgeway and viewing of the Uffington White Horse to top and tail it..
The chalk downland near Mere/Kingston Deverill in SW Wiltshire is excellent too - much more open/spartan but very atmospheric. You can combine that one with a trip to Stourhead.