Ustica's west side is dominated by the legendary Medico Rock (Doctor's Rock), visited for decades by many of the world’s most famous underwater divers. As it is a particularly extensive dive site, it can take as many as 5 or 6 dives to see it all. The underwater passage, at a depth of 20 m (65 ft) and running through the entire 70 m (230 ft) length of the rock, makes for a particularly interesting dive.

The tunnel is at least 25 meters (80 ft) wide and is sufficiently lit from the wide entrance to give a spectacular view of the exit together with a number of other openings in the rock where light filters through to create stunning luminous reflections.

Swimming in the company of large groupers, amberjacks and Mediterranean barracuda, at just a few metres underwater, particularly at the western point, is more or less guaranteed all around the rock, which is characterized by spectacular deep canyons where two-banded bream and corb have made their homes.