Enjoyable days out include
Sandingham House and Gardens
http://www.sandringhamestate.co.uk
Wimpole Hall
Deene Park
Duxford Aircraft Museum
Belvoir Castle
Belton House
http://www.nationaltrust.org.uk/main/w-vh/w-visits/w-findaplace/w-beltonhouse/
Althorp House & Grounds - Open July & August
Anglesey Abbey & Gardens
http://www.nationaltrust.org.uk/angleseyabbeyandgardenandlodemill.htm
Cambridge, Lincoln, Leicester, Northants are all no more than 1 hr away. Leaflets of all these and more are in the information centre on the CL.