RENTING AN INFLATABLE MOTORBOAT AND cruising the Baunei Coast is a great way to enjoy the many pristine beaches, electric-blue waters, and snorkeling areas that make this corner of Sardinia such a summertime destination. Most boaters, however, zip right past Grotta del Fico.

This 800,000-year-old coastal cave system, which winds through a sheer limestone cliff looking out onto the Tyrrhenian Sea, is only distinguished by a wooden staircase protruding from its mouth, 30 feet above sea level. It’s a beacon to all speleophiles, the geologically inclined, or anyone looking to beat the heat, if only temporarily.