A genuine modern wonder of the world, Hoover Dam was constructed in the 1930s and has gone on to capture the imagination of the American people. The facts and figures are staggering: the dam is 726.4 feet high, 1244 feet wide, 660 feet thick at the base, and was constructed with 3.25 million cubic yards of concrete. The water held behind the dam in Lake Mead, North America's largest man-made reservoir, meets the needs of more than 20 million people and generates huge amounts hydroelectric power. And yet nothing quite prepares you for the immensity of this awe-inspiring feat of engineering.
If you go:
It's still possible to drive across the dam but since the opening in 2010 of the Mike O'Callaghan - Pat Tillman Memorial Bridge, it is no longer open to through traffic; you can cross from Nevada to Arizona but you'll then have to turn around and come back the same way.
Links:

Nevada SR172
Boulder City, Nevada 89005 USA
Mailing address:
Lower Colorado Dams Office
P.O. Box 60400
Boulder City, NV 89006 USA
Phone Numbers:
Information
+1 (702) 494-2517
+1 (702) 494-2517
Toll Free
+1 (866) 730-9097
+1 (866) 730-9097
Message from RoadTrip America