Check out cycle route maps at https://cycle.travel/map
The cycle path is actually 20m to the North of the A299, behind the trees, so it cant be seen from the road.
It crosses the road on a footbridge, it's a surprisingly good path.
Note: if you are following it from West to East then ensure you follow the signs when it suggests you go up a little path alongside the road, otherwise half a mile later you will be lifting your bike over a gate
View attachment 466709
Cycle Path is on the left (North) side of the A299
There is a ditch, fence and trees between the path and the road, so you cant move between one and the other
View attachment 466710
@Trickedem and myself did that path a couple of years back on an Audax. Surprisingly good surface for cycling.

The B road through Cottenham is quieter than the A10 but still has far too many bad drivers close-passing. It's disgraceful that the Ely-Cambridge A10 has a cycle path - and again a not very good one - that still has a clanking great gap in it from Little Thetford to Waterbeach. Government is building another farking motorway to Cambridge when the cycleways (or cycle-friendly roads - I don't mind which) are still incomplete, demonstrating yet again that cycling is the lowest-priority opion.