The Balata dei Turchi is a wide flat slab of black lava that drops gently into the sea on the south coast, one of the few places on Pantelleria where you can actually walk into the water rather than dive off a cliff. The pool below the slab is more than ten metres deep, electric-blue, and almost always sheltered from the prevailing wind.
The road down to the cove is steep and rough, and the last stretch is on foot — sandals or grip-soled shoes are essential. There are no facilities of any kind, which is precisely the point: it's one of the most beautiful swimming spots on the island and you will rarely share it with more than a handful of other people.