A limestone outcrop explains the presence of the cave. The waters of Allt Smoo plunge into a funnel and reappear at the entrance of the outer cave. The latter, occupied during prehistoric and Viking times, can be visited at low tide by descending the wooden staircase near the car park. However, access to the inner caves is only possible to experienced, well-equipped potholers; fortunately, it is also possible to view the cave on a guided boat tour.