The park's landscape was built by two volcanoes. Piton des Neiges, now extinct, rises to 3,070 meters as the highest point in the Indian Ocean. Its collapse over millennia created three enormous calderas -- the Cirques of Cilaos, Mafate, and Salazie -- each a world unto itself, ringed by vertical ramparts hundreds of meters high. Piton de la Fournaise, one of the most active volcanoes on Earth, occupies the park's southeastern quarter. Its eruptions are frequent but relatively gentle, sending fluid basaltic lava flowing toward the sea rather than exploding skyward. The Plaine des Sables, the approach to the crater, resembles a Martian landscape: a vast expanse of oxidized volcanic rubble where almost nothing grows. In 2010, UNESCO inscribed the park's inner zone as a World Heritage Site under the name "Pitons, cirques and remparts of Reunion Island," recognizing both the terrain's visual grandeur and its exceptional biodiversity.

Isolation has made Reunion a laboratory of evolution. Roughly half of the island's plant species are endemic -- found nowhere else on Earth. The national park protects an estimated 900 indigenous plant species, of which 30 percent maintain intact populations. Among them are approximately 230 endemic flowering plants, including 120 orchid varieties that bloom primarily between November and April. The other half of the island's flora arrived by wind and ocean current from Madagascar and the African mainland, carried across hundreds of kilometers of open Indian Ocean to colonize volcanic rock. The park's forests range from lowland tropical woodland to high-altitude cloud forest, with altitude compressing ecosystems that on a continent would be spread across thousands of kilometers. Picking plants within the park is strictly prohibited -- a reflection of how fragile these populations are and how irreplaceable each species is.

Of the park's three great calderas, the Cirque de Mafate stands apart: no road reaches it. Roughly 800 people live in scattered hamlets accessible only by foot or helicopter, making Mafate one of the most isolated inhabited places in any European territory. The inner zone of the park, which includes Mafate along with the volcanic peaks and primary forests, covers about 60 percent of the park's area but holds fewer than 900 residents. The outer zone, at roughly 680 square kilometers, contains the more populated Cirques of Cilaos and Salazie, the plateaus, and approximately 75,000 inhabitants. More than 900 kilometers of marked trails cross the park, threading through rainforests, sugarcane terraces, and volcanic fields. Three long-distance trails approved by the French Hiking Federation traverse the park, with mountain lodges spaced along the routes. Over 400,000 visitors hike to the Piton de la Fournaise volcano each year.

The park's climate shapes every experience within it. Trade winds from the Indian Ocean strike the island's eastern face and are forced upward by the mountains, dumping extraordinary rainfall on the windward side. The leeward west enjoys drier conditions and clearer skies, making it the preferred approach for volcano hikes. Mornings typically begin sunny across the park, but by noon clouds build over the eastern slopes and push into the interior. By afternoon, the mountain regions are often fogged in, with rain persisting until evening before clearing again at night. The last snowfall on Piton des Neiges was recorded over two days in August 2003 -- a reminder that despite its tropical latitude, the island's altitude creates alpine conditions at the summits. The best hiking season runs from May to October, Reunion's winter, when temperatures are moderate and rainfall is at its lowest.

Reunion National Park was officially established on 5 March 2007 as the eighth national park in France and one of only three French national parks outside metropolitan France, alongside parks in Guadeloupe and French Guiana. The designation was decades in the making -- planning began in 1992. The park's main service town is La Plaine-des-Palmistes, population 6,626, which sits in the center of the park with visitor facilities and serves as a base for exploring both the volcano and the cirques. Access requires no fees or permits. Roads within the park are narrow and winding, climbing from near sea level to 2,500 meters in short distances. For the areas beyond the road network, hiking is the only option -- a constraint that has preserved some of the most spectacular wild landscape in the French Republic.