In reply to Dav79an:
Cwm Bychan is a lovely spot, secluded, quiet, and a great base to head up the Roman Steps into the Rhinogs, but the facilities are non-existent.
Gwern Gof Uchaf under Tryfan is very well-located for anything in Ogwen Valley, and does have loos and showers, but will tend towards busy at weekends with climbing club groups, etc.