Llyn Dulyn

Llyn Dulyn, the black lake, covers a red rock, Yr Allawr Goch. Of old, pouring water on this stone caused a fierce storm in the valley below, and it is believed that it may be the stone mentioned in the Mabinogion in the tale of Owain (or The Lady of The Fountain). However, the stone is now submerged, along with the causeway leading to it.
"there is a causeway of stones leading into this lake; and if any one goes along this causeway, even when it is hot sunshine, and throws water so as to wet the furthest stone, which is called the Red Altar [yr Allawr Goch], it is a chance if it do not rain before night. Witness, T. Prys, of Plas Iolyn, and Sion Davydd, of Rhiwlas, in Llan Silin.”
The lake is home to an unseen creature, and it has been suggested that this is an afanc. The creature has not been seen in recent years, but the complete absence of landing waterfowl suggests that it remains active.
A population of transdimensional blood salmon appears sporadically in the lake.