Kurobe Dam. Construction begin in 1956 and was opened in 1965.
Looking at the Toyama Side.
The tunnels, the ropeway stations and the cable car stations took 3 years to build with one small portion of a tunnel taking 13 months to blast through. That is dedication to bringing hydroelectric power to Japan.
During the warmer seasons you can access the observatory by climbing the stairs on the right. There was too much snow covering the stairs, so we climbed from the inside. There were over 100 (150? I can't remember exactly, I just remember that there were so many I thought it would never end!) steps to climb with an employee instructing you to rest at the halfway point.
But, the view was worth the climb! Just make sure to take a break halfway up and then continue.