The Gargano Peninsula's southern coast conceals more than sixty sea caves, a labyrinth of limestone grottos hollowed over millennia by Adriatic currents and winter storms. The largest, Grotta Smeralda, stretches forty meters into the cliff face, its ceiling pierced by a natural oculus that floods the chamber with refracted turquoise light between ten and noon each day. Geologists trace the limestone strata to the Cretaceous period, when shallow tropical seas deposited the calcium carbonate beds that now form Vieste's white cliffs. Vieste boat tour grotten excursions depart from Molo Sud, the southern pier of Porto di Vieste, where traditional gozzo boats—flat-bottomed wooden vessels designed for Adriatic fishing—navigate the shallow approaches to caves inaccessible by land. The route follows the coastline between Pizzomunno, the twenty-five-meter monolith marking Vieste's northern beach, and Baia delle Zagare, a twin-cove bay flanked by two offshore sea stacks. Mariners call this stretch the Costa del Sole, a twelve-kilometer arc where the cliffs rise vertically from water deep enough for boat passage within five meters of the rock face. The caves bear names drawn from local dialect and maritime history. Grotta dei Contrabbandieri sheltered smugglers during the Bourbon period, its double entrance allowing swift exits during customs patrols. Grotta Campana produces a bell-like resonance when waves compress air in its dome. Grotta Sfondata, collapsed at its center, forms a natural bridge with sunlight penetrating to the seabed eight meters below. Marine biologists document endemic species in these caves: the Adriatic sponge crab, the golden coral Savalia savaglia, and beds of Posidonia oceanica seagrass that oxygenate the coastal waters. The Gargano coastline holds UNESCO Geopark status, recognized for its karst topography and paleontological record. Summer sea conditions permit entry to the deepest caves, while spring and autumn offer clearer visibility for observing the limestone's layered geology. The traditional gozzo design, with its low freeboard and shallow draft, remains the most stable platform for navigating cave thresholds where wave action creates sudden surges.