Follow the Exter Ship Canal from the centre of Exeter to the River Exe Estuary. It's a nice easy cycle or walk following the canal towpath for about 5 miles.
The route starts near the cathedral in the city centre and heads south towards Topsham, passing River Exe Country Park and the Exe Reedbeds nature reserve. There's nice views of the River Exe and lots of water loving wildlife to look out for.
The route of the canal follows the Exe Valley Ride and the Exe Valley Way so there is scope for extending your exercise along these long distance paths. The Exe Estuary Trail also runs through the area.