Agios Nikolaos chapel on Palea Kameni island, one of the two historic volcanic islands in the center of the Santorini caldera (Greece). The sea around the island with its small bays is a popular destination for boat cruises - swimmers enjoy the warm waters of the red iron bay.
The orange stain of the rocks on the shore is the result of iron oxide deposit from an active hydrothermal vent system at the shallow sea floor around the Kameni islands. It releases heated, iron-rich waters and deposits a layer of iron-mud on the sea floor. (Photo: Tom Pfeiffer)