Sustrans NCN route 4 takes a diversion north at Melksham to take in the Chippenham-Calne railway path. Carry on eastwards following the signage towards Marlborough and you'll cycle right through Avebury.

If you've got a sturdy enough bike you can comfortably cycle the Ridgeway from the Sanctuary to Barbary Castle.

I was at Avebury for sunrise yesterday and then spent the day on the downs at the Polisher (photos to follow with a bit of luck) and on Mother's Jam. The Ridgeway was teeming with Mountain bikes.

NB. There's going to be a organised ride from Swindon along the Ridgeway next Sunday (I guess people were in training yesterday).