Elidir Fawr is mountain in Snowdonia, in the region of Gwynedd, Wales. Its elevation reaches 924 m (3031 feet). A small lake, Marchlyn Mawr, lies in the northern side of the summit. This lake is the upper reservoir for Dinorwig power station, which is hidden inside the mountain. The approach includesa reasonably short, but rocky walk up to the summit. The climb can be taken from Deiniolen, which offers views down to Llanberis, or from Nant Peris, which is a short and quite steep path. It can also be reached from Ogwen Cottage through a traverse of Y Garn and Foel-goch.