It's mainly on the sea prom, and down a few tracks etc, with the occasional bit of road use - we use the part between Gronnant and Prestatyn (prestatyn golf course) regularly with our young children when visiting the area (our 4 year old wouldn't ride her new bike until we took her on this section).
Llyn Crafnant is great. Nice cafe. If you want you can follow the fire road also. Saw alot of MTBers there this year but a lot further up from the lake itself. BTW I wouldn't recommend cycling from Trefriw: the hill is a KILLER!!