Piton de la Fournaise is a volcano on the island of Réunion, a French island in the Indian Ocean east of Madagascar, and it has erupted more than 150 times since the 1600s, one of the most active volcanoes on Earth and one of the few you can walk across between eruptions. The island is really two volcanoes stacked on the seabed, and the Fournaise is the young, still-burning one, rising 2,632 metres on the eastern side. The road climbs through green farmland into a moonscape of red and black cinder, the Plaine des Sables, and ends at a balcony on the rim of the Enclos Fouqué, the caldera that holds the volcano; from Pas de Bellecombe a steep metal staircase drops you straight down the cliff onto the caldera floor, and the green island disappears behind the wall. Ahead lies a plain of ropy black lava, marked with white paint splashes to show the way, and in the middle of it the little scoria cone of Formica Leo, left by an eighteenth-century eruption and climbed in ten minutes.
The walk across the Enclos to the summit takes about five hours there and back, over lava that crunches and rings underfoot, some of it only a few years old, to the rim of Dolomieu, the summit crater whose floor dropped more than 300 metres in a single collapse in 2007 and now fumes from vents in the dark. When the volcano is active the caldera closes and the show moves to the roadside: lava fountains and glowing rivers burn orange against the dark, watched from viewpoints far below, and on the eastern flank, the Grand Brûlé, the flows regularly cross the coastal highway and pour into the sea, so the road has been rebuilt over fresh rock again and again. Réunion is a French department, so the volcano has an observatory, a helicopter service and a bakery in the nearest village. Piton de la Fournaise is a volcano that erupts most years, and between them it lets you walk to the edge.