Sulphur Springs sits inside the collapsed western flank of the Qualibou depression, a seven-kilometer caldera that last erupted in the 1760s. The site releases hydrogen sulfide, carbon dioxide, and steam at temperatures reaching 170 degrees Celsius from fumaroles scattered across 45 hectares of barren, mineral-stained ground. Visitors do not approach the vents themselves. Instead, a network of concrete pools captures runoff cooled to 39–42 degrees Celsius, blended with spring water to produce a safe bathing temperature. The mud applied before immersion is volcanic clay rich in sulfur, silica, and trace minerals; guides distribute it from buckets at the pool edge. The Qualibou caldera formed roughly 40,000 years ago during a catastrophic eruption that reshaped the southwestern coast of St. Lucia. Sulphur Springs is the Caribbean's most accessible geothermal feature open to the public, marketed since the 1980s as the world's only drive-in volcano. The phrase is geologically imprecise—tourists drive to the caldera floor, not into an active vent—but it reflects the site's unusual topography. A paved access road descends directly into the depression, terminating at a viewing platform 30 meters from the primary fumarole field. The mineral content of the mud and thermal water has been studied by the University of the West Indies. Sulfur concentrations average 1,200 parts per million in the pools, high enough to produce the characteristic rotten-egg odor but below the threshold for skin irritation in healthy adults. The clay dries to a pale gray crust within minutes of application, then rinses cleanly in the thermal pools. Local operators describe the treatment as therapeutic for joint pain and skin conditions, though peer-reviewed clinical evidence remains limited. The site draws both independent travelers and passengers from cruise ships docked in Castries, 30 kilometers north. Sulphur Springs operates daily from 8:00 AM to 10:00 PM. The entrance fee is $12 USD per adult for the full mud bath experience, including access to the pools, a guided walk to the observation platform, and the application of volcanic clay. The facility expanded in 2019 to include changing rooms, freshwater showers, and a botanical garden planted with native heliconias and ginger lilies. Soufrière, the nearest town, lies three kilometers south along the coastal highway and offers provisions, fuel, and access to other geothermal sites in the Qualibou system.