As gusamc was trying to say, there is a route south from Swindon along the Ridgeway to Barbury Castle, which gives access to miles of byways and bridleways all over the Downs, across to West Woods, Avebury, Cherhill White Horse, Silbury Hill, and the Sustrans routes from Marlborough back to Swindon and through Calne and Chippenham to Bath and along the Kennett and Avon Canal to Devizes then Honeystreet, which can then get you on to the Wansdyke back towards The Downs and Swindon. There are many, many miles of tracks to enjoy south of Swindon, also the Ridgeway will take you all the way to Ivinghoe Beacon in Bucks.