My suggestion is: try everything. Think of things you could do, and do them. If you don't enjoy somthing, you don't need to do it again. Go from one thing to another, and you'll find stuff you enjoy. And if you stop enjoying it, stop doing it and try something new.
Things that spring to mind are, swimming, joining a local ramblers' group, selling stuff on ebay, learning a language, taking a night class, doing a degree with open university, painting, visiting local historical sites, cycling, invite some friends round for a game of scrabble, learn to play the harmonica, do a few hours' work at your local charity shop, do some wood carving/whittling, choose books at random (non-fiction) from your local library, buy a digital camera (if you don't already have one), explore public footpaths with a friend (you can probably borrow landranger maps from your local library), take some bird/plant/insect books with you and learn about the things you can see, join every local club, group and society you can, and see what happens.