I recommend the Gwydyr Forest area, starting in Betws-y-Coed. If I remember right, the entrance to the best trail is just behind the Ty Gwyn Hotel, it is a bit of a steep start but the rest of the walk is quite level.
While there last year, we spent an hour watching a red kite circling and swooping, in a clearing just outside the forest. Also spotted loads of orange tip and blue butterflies. There are quite a few good B&B's in Betws-y-Coed, too.