A very large natural cave with its main chamber (40m wide, 15m high, 83 m long) was created by the sea (and the entrance is at the end of a 600m tidal gorge that was once part of the cave until its roof collapsed).
It is unusual (and may be unique in the UK) because although the main chamber was created by the sea it connects to a series of inner chambers created by the action of freshwater.
The cave is dry except during spring tides. The cave comprises the main cave, a chaber with a 20m waterfall and a short freshwater passage leading to a sump.