I live in Histon. There are various local loops I can point you at. Email in profile.
But the honest truth is that if mountain biking is what you want, you’ve really chosen the wrong county.
Most of the riding I do from my front door is on the road bike as there’s just a lot more to do.
Some possibilities though:
– Thetford (as above)
– There’s a nice loop starting from the Roman Road (South side of Cambridge) and off to the grain silos at Linton
– Harcamlow way is local and not bad for a quick blast; various variations on this.
– There’s some moderately interesting stuff once you get beyond Wimpole (probably better on a CX bike)
– The Alps are only about a 10 hour drive away….