The movie Colossus was a 1960s or 70s movie.
And I'm kind of inclined to believe them because, look, in the 1960s, right, where they're from,
Especially if you're going back to the 1950s and 1960s.
Well, these massive labyrinths that exist underground were all flooded in the 1960s accidentally when they created dams in order to provide irrigation to agriculture that was in the area.