Trafalgar Falls are twin cascades in the rainforest of Dominica, a short walk up from Roseau. They land in a single field of boulders where you can sit in cold water and hot water at the same time. Two rivers arrive at the same cliff. The taller fall is called the Father, the fuller one the Mother, and they come down side by side into the same green volcanic gorge. Getting to the viewing deck takes ten minutes of humid path under tall forest, past ferns and heliconias, with hummingbirds working the flowers and most of the birds you can hear staying out of sight. Past the deck it stops being a path. The rest is a clamber over giant boulders slick with spray, and at the bottom the two cascades come down close enough together that talking stops being worth the effort.
The heat does not come from the falls. It comes from underneath: Dominica sits on one of the most geothermally active stretches of the Caribbean, where rain sinks into porous volcanic rock, is heated deep down by magma and pushes back up as sulphur-rich springs. At the foot of the Father those springs seep between the boulders, streaking the stone ochre and yellow and warming pockets of water an arm's length from the cold plunge pool under the falls. Guides from the village know which pocket is which, and your afternoon goes in moving from one to the other and back. From June to November the rains swell the pair into a brown torrent, fullest between August and October, and the boulders turn dangerous enough that most people watch from the deck instead. The same underground plumbing feeds the sulphur springs at Wotten Waven and, a hard six hours' walk away in the same park, the Boiling Lake, a flooded volcanic vent of grey churning water that has drained and refilled after nearby earthquakes. The warm pocket you are lying in comes off that furnace.