About a 45-minute drive from Las Vegas on U.S. 93, the Hoover Dam is one of America's greatest engineering feats, and considered one of the seven wonders of the industrial world. Guided tours run from 9 am to 5 pm in the winter, and 9 am to 6 pm in the summer, and require a screening process similar to airport security, after which you'll be led through a series of interesting exhibits and vantage points. You can also walk or drive the top of the dam, though you do have to remain in your car after sunset.