The area around St Ives has some of the finest walks in Cambridgeshire. The region is generally flat so walking is quite easy.
However there are some wonderful walks, especially along the Ouse Valley.
The most popular of these walks is the 6 mile round trip from The Old Riverport along the Thicket path to Houghton. It continues across the flood meadow to Hemingford Abbots and back to St Ives through Hemingford Grey. Most of the year the walk enters St Ives by the Dolphin Hotel across Hemingford Water Meadow, however as it's name suggests, the meadow is often flooded during winter months so the route continues along the St Ives and Hemingford Roads and Filberts Walk.
There are several websites dedicated to walking in Cambridgeshire.
This one http://cambswalks.blogspot.co.uk/ lists 6 walks all in and around St Ives.