Llyn Peris is a lake in Snowdonia, Wales, approximately 1.8 km long and situated close to the villages of Llanberis and Nant Peris, and the smaller twin of Llyn Padarn. The lake was formed glacially and is an example of a moraine-dammed lake. Llyn Peris is named after Saint Peris, an early Christian saint of whom little is known. The lake is flanked on one side by the mountain Elidir Fawr and the former slate quarry of Dinorwig. Above the opposite bank are the hills of Derlwyn and Clogwyn Mawr and a rock formation known as the Lady of Snowdon, due to its resemblance to a human face. The ruins of Dolbadarn Castle are also located on a mound above the lake.