To the northwest of the main Tremadog area, this fine mountain-crag features a wonderful slab of rock and offers a good set of routes across the grade range. The setting is magnificent above the twin tarns of Llynnau Cwm Silyn, and the delightful approach walk only adds to the day. The crag is correctly called Craig yr Ogof, but usually referred to by climbers as Cwm Silyn.