|Nice easy route, there's a small disused chalk pit just after Wimpole thats good fun, got a few runs into the pit, can be a good half way point mess about rest area, there's some chairs there to rest on aswell. There is a fun bit of windy wooded singletrack that goes on for about a mile or so and ends in some small bomb holes which are another good bit of fun. After this wooded section, its mostly road riding to get back into Cambridge.
Head out from central cambridge towards cotton, then on from cotton to little Eversden, then across to Wimpole, you'll need to get off and push your bike through the grounds of Wimpole out of respect. Head out of Wimpole to Orwell and then your at the chalk pit, after the pit, head back down the road toward Barrington, but head off road and up the hill at the sharp corner, then into the woods for some fun windy singletrack and finishes in some small bombholes and a good fast downhill bit (beware of the gate at the bottom which has to be kept shut!), Out onto the road again and head over towards Grantchester, then back up to central cambridge.