Start at LLanrwst car park,follow marin until the road crossing after the dragons tail,turn right down to the ugly house,across the river turn right,turn left at capel tan-y-garth,tech climb over to dolwyddelan-DO NOT TRY RIDING BWLCH Y GROES-unless you like knee deep bog death marches-cross river left past school and follow railway to tan aeldroch,right up past ty mawr until you cross loop2 of penmachno,quick lap of machno til you rejoin where you started,retrace route back to tan aeldroch but cross river ,left to pont y pant,turn right and follow sarn helen, over the miners bridge,straight across road until crossed by marin trail,follow marin back to car.80.3km and a lot of climbing.One of my regular rides-takes me 5 1/2-6 hours on the ss.Enjoy.
Can always come off at Cyffty Tube and go llyn geirionydd,llyn crafnant,roman road to capel curig then ugly house etc for a bit extra.