I visited the Hoover Dam back in the early 90's. I was blown away by the sheer size of it.
I was young (in my 20's) and thought 'what's the big deal? it's just a dam.'
Let me tell you - I recommend to everyone to see the Hoover Dam.
PBS has an excellent link for more information: http://www.pbs.org/wgbh/amex/hoover/
Here are some fast facts from http://www.pbs.org/wgbh/buildingbig/wonder/structure/hoover.html
At its base, Hoover Dam is as thick (660 feet) as two footballs fields measured end to end.
Hoover Dam is 726 feet tall. That's almost 200 feet taller than the Washington Monument in Washington, D.C.
During peak periods of electrical demands, enough water runs through the generators to fill 15 average-size swimming pools (20,000 gallons each) in one second.
There is enough concrete in Hoover Dam (4.5 million cubic yards) to build a two-lane road from Seattle, Washington, to Miami, Florida, or a four-foot-wide sidewalk around the Earth at the Equator.
The Hoover Dam is so thick and heavy, it doesn't even need to be curved! It's heavy enough to resist the weight and thrust of the water pushing behind it, but designers thought people would feel safer with a curved design.