On Gozo's south coast, west of Xlendi Bay, a huge natural sea arch cuts into the rugged cliffs — a cathedral-like cave of raw, weathered rock quite unlike the smooth pale grottoes elsewhere on the island. It has no official name and no path from land: the only way in is by water. Launch a kayak from Xlendi Bay and paddle roughly a kilometre along the Sanap cliffs, and you'll round into a wide, shaded chamber opening onto deep turquoise water. Inside there's room to swim, snorkel along the rocky edges, or climb the pitted ledges for a cliff jump into the clear blue below. There are no facilities and the sea is the only access, so pick a calm day, bring water and shoes with grip, and check the swell and wind before you set off.