The Benagil sea cave sits 150 metres inland from the waterline, its dome carved by 20 million years of wave percussion into the Algarve's Miocene limestone. Two openings frame the chamber—one at sea level where boats enter, one overhead where sunlight falls through a collapsed roof onto the sand below. The vault measures roughly 20 metres across, its interior lit amber and ochre when morning sun angles through the oculus. Geologists attribute the twin apertures to differential erosion: softer calcarenite layers dissolved faster than the harder dolomitic bands that form the cave's ridgeline today. Albufeira dolphin watching and Benagil cave excursions depart from Marina de Albufeira, a sheltered harbour built in the 1980s to replace the town's original beach-launch fishing fleet. The marina lies 2.4 kilometres west of the old town, accessible by a dedicated shuttle route that runs every 20 minutes in season. Common dolphins—Delphinus delphis—hunt the offshore waters year-round in pods of 10 to 40 individuals, their presence driven by sardine and mackerel schools that follow the Canary Current northward along the Portuguese coast. Bottlenose dolphins appear less frequently, typically in smaller groups closer to the shoreline where rocky reefs concentrate prey. Sightings peak between May and September when sea surface temperatures exceed 18 degrees Celsius and plankton blooms draw baitfish into the photic zone. Speedboat operators cover the 9-kilometre route to Benagil in under 30 minutes, pausing mid-journey when dolphins surface. Traditional wooden boats—modelled on the Algarve's historic bote de sardinha—take 50 minutes, their slower pace allowing longer observation windows. Both vessel types navigate the same coastal corridor, passing Praia da Marinha's twin arches and the Alfanzina lighthouse before entering the cave through its seaward mouth. Portuguese maritime law prohibits engine use within 50 metres of marine mammals, so captains cut throttle and drift when pods approach. The Benagil chamber itself permits entry only in calm conditions—swell heights above 1.5 metres force cancellations, a constraint that affects roughly 15 percent of scheduled departures between October and March. The cave's sand floor sits dry only at low tide, a two-hour window that shifts daily with the lunar cycle. Tour operators time departures to coincide with mid-tide, when water depth inside the vault reaches one metre—shallow enough for safe manoeuvring, deep enough to float without grounding. The oculus above measures 12 metres in diameter, its edge fringed with ice plant and sea thrift that bloom purple and white from April onward. Albufeira dolphin watching and Benagil cave tours typically allocate 10 minutes inside the chamber before returning via the same coastal route, though weather and pod activity influence the exact itinerary on any given morning.