Kurobe dam was built at the end of the 1950’s and many people died (over 150) in the making, it is the tallest dam in Japan. This was made to face the rapid growth of needs in the industrial expanding Japan at the time.
It remains a hot spot for visits for japanese families. It becomes also a trending spot for tourist groups who combine with the Alpine Route (Tateyama)
I did the tour combined with the Alpine route but I must say this was too much of a heavy day, starting at 5am in Toyama and coming back at 20h00.
My recommendation is to do the tour on a one-day tour from Nagano and enjoy the view, the fresh air and the altitude. take your picnic as there are little options for food there. of course, many vending machines available!