At a place called Pwllhelig you will find what has been described as a “dark pool”. There once stood a house at this site, and its owner was described as evil. It is said that the house collapsed into a crevasse following a landslip, and a spring filled the gap with water. Since that time, a Lady in Black was said to haunt the area. She is said to be seen wringing her hands and moaning to herself.
For further information, please read Haunted Wales: A Guide to Welsh Ghostlore by Richard Holland.