The Montrebei Gorge is a place that is located between the provinces of Huesca and Lleida (Spain), between the regions of Ribagorza and Pallars Jussà.

It is constituted in the narrowest part through which the Noguera Ribagorzana river, which constitutes the natural border between Aragon and Catalonia, crosses the Montsec mountain range, vertically falling walls of more than 500 meters and a width at its minimum point of 20 meters .

The Catalan part is part of the Natural Reserve of La Noguera. It is within the Area of Natural Interest of the Sierra del Montsec.

It was acquired in 1999 by the Fundació Territori i Paisatge with the aim of preserving its natural and landscape values.

On the Aragonese side, the right bank of the river extends to the north of the gorge, the tower of Chiriveta Castle and two Romanesque churches: Nuestra Señora del Congost and Nuestra Señora del Congost Vieja (in ruins).

In the Catalan part, the passage through the gorge is made entirely by a path dug into the rock, and at some points by tunnel. To the south, the path gains altitude and runs along the slopes of the mountain until we see the reservoir.

The Mont-Rebei gorge, which occupies an area of ??600 hectares, constitutes one of the most unique natural spaces in the Pre-Pyrenees, both from a landscape point of view, as it is the only large gorge free of infrastructure, and because of its great biodiversity.