"In the heart of Morne Trois Pitons National Park bubbles this deep, flooded fumarole—the second-largest of its kind in the world. The hike to this dramatic, blue-grey cauldron traverses steep, rain-forested river valleys and skirts around mudpots veiled in steam. The 8.1-mile roundtrip is best navigated with a local guide. Heed trail closures and never swim in the lake. The temperature occasionally drops, but scalding water and harmful gases could erupt at any time with no warning."