Hoover Dam
is really Hoover Dam, Boulder City, NV
Real place, still recognisable
Real-world photo: Wikimedia Commons
In the game
The NCR's prize and the stage for the final battle between the NCR, Caesar's Legion and whoever you sided with.
The real place
Completed in 1936 on the Nevada–Arizona border, it holds back Lake Mead.
Visiting
Take a dam tour, then walk the bypass bridge for the best view of it.