At a glance
Saint-Denis is the gateway, but Réunion works as an island-wide trip. Piton de la Fournaise, the Plaine des Sables and the cirques of Mafate, Cilaos and Salazie call for several bases rather than one hotel.
The real cost
A car makes the trip much easier: the main trailheads are spread out and public-transport connections take time. Food and rentals remain more expensive than in mainland France.
What nobody tells you
Weather changes from one side of the island to the other, and cloud builds quickly in the highlands. Start hikes early, after checking trail conditions and volcanic activity.