Pal and I thinking of heading out for a long weekend.
We're in Edinburgh. Were thinking of a train to Berwick, Newcastle or Durham and then riding across towards Penrith or Carlisle and getting the train or bus back home.
Don't really know that area at all - any suggestions?

Quiet roads, paths or light single track preferred - will be on cyclocross bikes or rigid hardtails

Pennine Cycleway perhaps? Runs from Berwick to Kendal. https://www.visitlakedistrict.com/thing ... 8-p1213381

From Berwick you could follow the Sandstone Way, which starts with the NCN route down the coast, then goes inland and up Coquetdale. From Alwinton there are a few options depending on conditions, how much you're willing to tolerate a bit of rough stuff to avoid road, and firing on the ranges to cut across to the end of the forest drive on the A68 to take you over to Kielder. From Kielder, you can take the cross border route to Kershopefoot and then some (very) quiet lanes towards Carlisle.

Hmmm, that Sandstone Way looks pretty interesting!

I did it for a second time earlier this year. I didn't have a great time the first time (there's an unfavourable write-up on here somewhere if you search), but doing it in a group (gates!) and in the dry made a lot of difference. There are still some small sections I'd skip, particularly if it's wet, where there's excessive gateage/bogs for minimal gain. I'd be happy to point them out to you.