There are some lovely walks around the the Town of Thrapston. The old railway tracks have been used to provide the Town Walk which takes you along the side of the Thrapston Gravel Pit, a wonderful site for seeing wildlife, especially migrating birds. It joins up with footpaths that will take you through Titchmarsh Nature Reserve and then along the Nene Way to Aldwincle and Wadenhoe (where you can stop for a pint of local beer and lunch at the Kings Head before heading back again!)
From Thrapston you can take footpaths through Islip and then on to Lowick and Sudborough or up into the woods and all the way to Lyvedon New Bield.
Travelling over the Nine Arches Bridge, there is a footpath to the left across the water meadows, over the disused railway, bear left for 100 yards or so and then under the A14, (it is a clear cart track) until you are on the other disused railway track that will take you all the way to Stanwick Lakes. This track is an excellent cycle track and suitable for young riders.
As with all these walks it is useful to have an ordinance survey map of the area showing all the footpaths, bridleways and byways as it easy to take a wrong turn and become lost, or walking a lot further than planned to get home.