Aldreth causeway - do tell. I've only ever got to Haddenham and turned the other way towards Grunty Fen.
Grunty Fen is special in its own way, isn't it... Aldreth Causeway: there's a byway from near Rampton to Aldreth. The section from north of the river (there's a bridge!) to Aldreth is labelled on the OS map as "Aldreth Causeway", but the bit from near Willingham is fun. It doesn't look particularly special from my photos, but I like it:
and there's a climb into Aldreth! Which is quite exciting in its own way. You can see the wind turbines at Balsham clear as anything - suddenly becomes clear why they're there, catching all that lovely wind off the Fens.
There's a lovely description here:
https://ericwark.com/2020/11/29/the-aldreth-causeway/I am loosely planning on leading a CTC ride along it this year - hopefully a Thursday sometime in May, before the grass gets too high, but I haven't got anything in the diary yet. Will update here nearer the time in case anyone is interested in joining us!