A high mountain cwm tucked underneath the South ridge of Snowdon/Yr Wyddfa that is popular with walkers on the Watkin path but not well-known by climbers. Clogwyn Du is the main cliff of interest providing long mountaineering routes and traditional Winter gullies. Also within the cwm is the Gladstone Slab and the long forgotten Craig Ddu.
Park at the National Park pay & display car park in Nant Gwynant and follow the Snowdon Watkin path into the cwm. The Gladstone Slab is the obvious slab beyond the Gladstone rock, Craig Ddu is the broken crag above the slab. Clogwyn Du is reached by following the Watkin path around into Cwm Tregalen and heading directly uphill from the ruined buildings on the left.