The Trou de Fer ("Iron Hole") is a canyon on Reunion Island, off the coast of Madagascar in the Indian Ocean. The primary river flowing through the gorge, which is up to 300 m (1,000 ft) deep, is the Bras de Caverne River, a tributary of the Rivière du Mât.
The canyon has two distinct parts: a large crater, which is fed by six prominent waterfalls, and a narrow slot canyon at its outlet, which constitutes most of the canyon's length. The canyon starts at the waterfall of the Bras Mazerine stream and after some 1.4 – 1.8 km from the left side joins the main Bras de Caverne stream.