Not Just Norway
In Missouri they leveled the top of its highest "mountain" and built a reservoir. During the night at low demand, water is pumped up from the river below to the reservoir. During the day the water flows down through a pipe bored down through the middle of the mountain and spins the generators.
Built in the 1960s. It's very odd to stand on top of a mountain well above everything else around and gaze across a huge sheet of water at eye level - like an infinity pool gone beserk.