The gigantic Gruta de Benagil sea cave (Benagil Cathedral), Algarve, Portugal

The Piusa sand caves, Setumaa, Setu county, Estonia, Baltic States, Europe

Small west coast black sand beach resort, popular for its caves and cliff walk, Ajuy, Pajara, Fuerteventura, Canary Islands, Spain, Atlantic, Europe

Purple heather on the cliffs above Smoo Cave near Durness which has one of the largest sea cave entrances in Britain, Durness, Highlands, Scotland, United Kingdom, Europe

Drone view of Matala artificial caves on the rock by the beach at Crete, Greek Islands, Greece, Europe

Small west coast black sand beach resort, popular for its caves and cliff walk, Ajuy, Pajara, Fuerteventura, Canary Islands, Spain, Atlantic, Europe

A cave entering the water from the beach at Praia da Coelha, Algarve, Albufeira. Portugal

Qumran Caves, Qumran, Israel

Kalalau Beach, viewed from a cave, Na Pali Coast State Park; Kauai, Hawaii, United States of America

Woman standing under the large, boulders on the seaside shores of The Baths, a famous beach in the BVI's, Virgin Gorda, British Virgin Islands, Caribbean

Common stingray (Dasyatis pastinaca) inside Gruta azul dive site, eastern coast of Santa Maria Island, Azores, Portugal, Atlantic Ocean

Eye of a tawny nurse shark (Nebrius ferrugineus), Close-up of the eye of a sleeper shark lying on the sand in a cave in the south of the Mayotte lagoon at a depth of 55 meters.