National Cycle Network Route 26
The entire route covers approximately 28 miles and is manageable in a day, but you can do as much or as little as you please. The route includes the towns of Dorchester and Sherborne and many pretty villages along the way.
Although most of the NCN Route 26 is signed, you should use Ordnance Survey Landranger maps 183 and 194.
The route details are in a north to south direction from Sherborne to Dorchester. But you can cycle the route in either direction and do as much or as little as you please.