Fort de l'Infernet, Military fortification in Briançon, France.

This stone masonry fortress stands at 2,380 meters altitude on a rocky outcrop, commanding panoramic views over the Durance valley and surrounding alpine terrain in the French Alps.

Constructed between 1876 and 1878 as part of the Séré de Rivières defensive system, this fort served as France's last stone-built military installation before modern construction methods emerged.

The name Infernet comes from "Petit Enfer" (Little Hell), after the lightning that often struck the summit; a small obelisk at the top marks a soldier killed by lightning in 1934. Inside, visitors can still see beds, a stove, doors and shutters left in place, and a François-Vaillant model C or D stove whose cooking pot tub sits on the ground nearby.

The fort is reached on foot from Briançon; the route climbs to 2,377 m, so allow for altitude and changeable alpine weather. Inside, the path from the north-west entrance makes two hairpin bends past the powder magazine before reaching the summit courtyard, and the barracks and gun platforms stand on terraces at different levels. Guided tours are offered; check locally before setting out.

Fort de l'Infernet holds the distinction of being France's final fortress constructed entirely from cut stone masonry, marking the end of an architectural era in military construction.