Nottingham is about 20-30 miles west of Grantham. I took a day trip there from Grantham. There you'll find Notthingham Castle, Robin Hood's Major Oak, and more. The picture shows a statue of Robin Hood found near Nottingham Castle.
In Nottingham, you'll also find Ye Olde Trip to Jerusalem. It's a very old inn found near the castle. Like it says on its walls, it's the oldest pub in England (est. 1189.) I'll take their word for it...I guess. http://www.yeoldetriptojerusalem.com/
Belvoir Castle - about 6 miles from Grantham. Even though it's spelled BELVOIR, locals refer to it as Beaver Castle...not sure how they got Beaver from Belvoir. The place has some history to it; the original owner was an associate of William the Conquerer. The structure that stands there now dates from the 19th Century. It's a nice place to tour through - nice architecture, furnishings, art, and garden.