The Algarve coastline shelters more than 200 sea caves, carved by millennia of Atlantic swells into soft Mesozoic limestone, but only one—Benagil—opens its vaulted ceiling to a shaft of daylight that illuminates the sand floor below. Thirty kilometres offshore, the continental shelf drops sharply to 200 metres, creating nutrient upwellings that draw common dolphins, bottlenose dolphins, and seasonal fin whales into coastal feeding grounds year-round. Tour operators began combining cave access with cetacean observation in the early 2000s, recognising that the same offshore currents that sculpted the rock also sustain the marine mammals travellers hoped to encounter. Today, an Algarve dolphin cave tour departs from three principal marinas—Albufeira, Portimão, and Vilamoura—each positioned within fifteen nautical miles of both Benagil Cave and the prime dolphin corridor that runs parallel to the Ponta da Piedade cliffs. Morning departures align with calmer sea states and higher cetacean activity; dolphin pods feed most actively before midday, when smaller fish schools rise toward the surface. Marine biologists now accompany a growing share of cruises, providing real-time species identification and explaining the behavioural cues—synchronized surfacing, bow-riding, coordinated feeding arcs—that distinguish resident pods from migratory groups. The caves themselves are not static monuments. Benagil's iconic dome continues to widen as wave action undercuts its walls; smaller grottos along the same stretch—Gruta do Capitão, Algar Seco—display honeycombed erosion patterns and tidal benches that shift with each winter storm season. Operators navigate these features under strict coastal protection guidelines established in 2019, which prohibit anchoring within cave perimeters and limit the number of vessels entering Benagil simultaneously to six. The regulations preserve both the geological formations and the acoustic environment dolphins require for echolocation. Benagil Cave cruises now represent the most-booked marine excursion category along Portugal's southern coast, yet sighting success remains contingent on seasonal variables and sea conditions rather than operator schedules. The integration of marine science into commercial tours has elevated visitor understanding: passengers learn to distinguish common dolphins' rapid, playful leaps from bottlenose dolphins' slower, deliberate surfacing, and to recognize the blowhole mist of a distant fin whale before the animal's dorsal ridge breaks the horizon.