These protruding banks resemble man-made causeways and have long been part of the centuries-old legend of Cantre'r Gwaelod, a fabled sunken kingdom which was lost beneath the waters of Cardigan Bay.

The legend of Cantre'r Gwaelod is comparable to the deluge myth found in nearly every ancient culture, and it has been likened to the story of Atlantis[by whom?].

In a 2006 episode of the BBC television documentary Coast, presenter Neil Oliver visited Sarn Gynfelyn to explore the legend of Cantre'r Gwaelod.

The programme also featured the remains of the submerged forest at Ynyslas, some 5 miles (8.0 km) north of Sarn Gynfelyn, which is also associated with the legend.

The vista of dead oak, pine, birch, willow and hazel tree stumps preserved by the acid anaerobic conditions in the soil is revealed at low tide and is estimated to be about 5000 years old.