This wood near Grantham has miles of footpaths taking you to conifer woodland, grassland and the lovely Twyford Wood butterfly glades. Here you can look out for dingy and grizzled skipper butterflies.
The site is a former second world war airfield with a control tower and wide open runways which are good for cycling. There is a small car park at the northern end of the forest where you can pick up the trails. The woods are very close to Colsterworth and Woolsthorpe-by-Colsterworth, the birthplace of Sir Isaac Newton. Here you can visit the 17th-century limestone house of Woolsthorpe Manor which is owned by the National Trust. This is said to be the site where Newton, observing an apple fall from a tree, was inspired to formulate his law of universal gravitation. The village and manor are only about a mile from the woods. It's a nice place to go for refreshments and to learn about the history of the area after your walk.
The Viking Way passes through nearby Buckminster so this is a good option if you'd like to extend your walking in the area.