The Hoover Dam is one of the wonders of the modern world. It is located about 30 miles (48 km, and less than an hours drive) southeast of Las Vegas, on the Nevada-Arizona border. It was originally named the Boulder Canyon Dam, but was changed to the Hoover Dam, named after Herbert Hoover. He was the one to propose the project in 1921 while he was Secretary of Commerce, and then initiated the project in 1930 as President of the United States.
The purpose of the dam was regulate the Colorado River, which would sometimes overflow after the Rocky Mountain snow melted and filled the river. These floods would them threaten communities down river. Also, in building the dam, Lake Mead was created, which is now the largest reservoir in the US. When the generators are operating at full power, the dam now produces enough electricity to supply a city of 750,000 people.
Construction began in 1931, and continued until 1936, being completed 2 years ahead of schedule. During the course of the project, it took a total of 16000 people working 24 hours a day to finish. Most of these workers lived in tents and shacks nearby. And contrary to rumors, no one is believed to be buried in the dam. The dam is 660 feet (200m) thick at the base, and 45 ft (15 m) at the top. And at 726 feet tall, it is quite a bit taller than the Washington Monument.
If you want to visit the dam, there is a Visitor's Center which shows films of construction and also operates tours. Keep in mind though it is now one of the most visited attractions in the country, and it can be quite busy. The road coming in from both sides is very curvy and steep as you descend into the canyon, so traffic moves very slow, and because of the amount of visitors, sometimes it can take hours to even reach the dam. And it is one of the few places to cross in the area, so regular through traffic has use the same roadways, making it a bit of a hassle.