The Santorini caldera is not a bay but the flooded heart of a Minoan-era volcano that erupted around 1600 BCE, collapsing into the Aegean and leaving a 300-metre-deep basin ringed by cliffs. The event is often linked to the demise of Thera's Bronze Age civilization and the possible origin of the Atlantis myth. Today the basin remains geologically active — Nea Kameni, the black island at its centre, last erupted in 1950, and fumaroles still vent sulfurous steam along its western slope. A boat tour Santorini caldera typically departs from Fira Old Port, 587 steps below the clifftop town, and crosses to Nea Kameni for a guided volcano hike. The ascent takes 20 to 30 minutes over sharp basalt and pumice, rewarding visitors with close views of the crater and panoramic sweeps of Santorini's crescent. From there, most cruises continue to Palea Kameni, where thermal springs tint the sea rust-orange near the shore; water temperature hovers around 30–35°C year-round, warmer than the surrounding Aegean by several degrees. Catamaran and traditional schooner itineraries extend the experience beyond the volcanic islands, sailing beneath the red cliffs of Akrotiri or stopping at Thirassia, the least developed fragment of the ancient caldera rim. Sunset departures time their route to position the boat off Oia as the sun drops behind the clifftop village, a vantage that avoids the crowds congregating on land. Onboard service ranges from simple refreshments to full barbecue spreads and open bars, depending on operator and vessel class. The conservation fee of five euros per person — collected in cash at Nea Kameni — funds trail maintenance and monitoring of the active geothermal zone. Morning departures between 09:00 and 12:00 benefit from calmer seas and cooler hiking conditions, though afternoon and evening sailings trade comfort for dramatic light. The caldera's depth and exposure to the meltemi wind mean swells can pick up quickly; those prone to seasickness should plan accordingly.