You can get down into Ceunant Llennyrch from Coed Felinrhyd woodland. In which case, from the A470 turn into Maentwrog, go right through and keep going. There's a layby on the right just before the hydro (on the left) park in the layby and cross the road through the wooden gate following the signs into the woodland. There may well be other routes but I have parked there many a time and it is perfectly safe to leave a car there. There's plenty of space for several vehicles.All the best.