Hoover Dam is 726 feet of concrete wedged into Black Canyon, about thirty-five miles southeast of Las Vegas, and it is still the most impressive thing a person can drive to in an hour. It was finished in 1936, five years into the Depression, and Lake Mead backed up behind it.
Three levels of visit are sold. The self-guided visitor center gets you the exhibits, the film and the observation deck. The guided powerplant tour adds an elevator ride down into the Nevada wing to stand beside eight generators the size of houses. The longer guided dam tour goes further in, through the original construction and inspection tunnels inside the dam itself, with a look down a ventilation shaft to the river.
The powerplant tour can be booked online. The dam tour cannot — it is sold on site only, on the day, first come first served, and it sells out. The Mike O'Callaghan–Pat Tillman Memorial Bridge downstream has a walkway with the best view of the whole thing, and costs nothing.