Divers from around the world come to explore Ustica's magnificent underwater sites. The island's western shores are home to a protected marine reserve, which is divided into three zones. Highlights include the underwater archaeological trail off Punta Cavazzi, where artefacts including anchors and Roman amphorae can be admired. Other popular dive sites are the Scoglio del Medico, an outcrop of basalt riddled with caves and gorges that plunge to great depths; and Secca di Colombara, a magnificent rainbow-coloured display of sponges and gorgonias.

The island's many dive centres organise itineraries and hire out equipment.