Why not call into Keswick Mountain Bikes (in Keswick, strangely) and pick up a leaflet called “Biking Around Keswick”. It’s free and you can also talk the guys in the shop about current conditions – they’re really helpful.
The leaflet opens out to an A3 OS map (1:50,000 slightly shrunk) and it shows 4 routes with written directions/turning points:
– The Skiddaw Loop (28 km, moderate)
– Lonscale Fell & the Glenderaterra Valley (18 km, moderate)
– The Borrowdale Bash (the correct version that @d45yth refers to) (28 km, harder)
– Old railway line (10 km, family friendly so probably not what you’re looking for).
Can’t comment on the routes, I’m afraid but I’ll be doing the Bash and Skiddaw Loop for the first time next week when I’m up on business 😛
HTH
Stu