The Saint-Clair run-of-river hydroelectric power plant was built in a cave inside the mountain, below Ussel Castle: for this reason, its inclusion in the surrounding environment is particularly impressive. Its capacity amounts to 31 MW.

The plant went into service in 1950. Today, the diversion canal reaches the inside of the mountain and there is also the forebay reservoir, from which the two penstocks sunk in the rock leave to feed the units. There are two access tunnels to the engine room in the cavern: a driveway tunnel for transporting materials and a pedestrian tunnel, through the service rooms.

The driveway tunnel originally handled 132 kV production cables, to the outside station, when the step-up transformers were also placed in two niches within the same tunnel. Currently, only the medium-voltage busbars remain, as the transformation of water energy into 100 percent renewable energy has been moved outside to the new power station.

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