The valleys of North Snowdonia.
Cymoedd literally means "valleys" (with cwm being the singular form), though in North Wales, it is usually reserved for glacial valleys. The area we were staying in was a series of glacial valleys that separated the major mountain massifs.
Ok, so strictly speaking, it is a hill between Afon Glaslyn and Nanmor, but given the size of the mountains on either side, it feels like part of the valley.