The Hoover Dam is the reason Boulder City exists and the reason most visitors stop here. The concrete arch-gravity dam holds back the Colorado River to form Lake Mead and remains one of the great engineering monuments of the 20th century — 221 metres tall, with Art Deco detailing on every visible surface, including the floor mosaics, the elevator doors, and the bronze figures of the Winged Figures of the Republic at the entrance.
Two tour options run daily. The shorter Powerplant Tour takes you down into one of the generating wings; the Dam Tour goes further, through the tunnels carved through the dam itself. Both fill up by mid-morning in summer — book online or arrive at opening. There is also a free observation deck on the Memorial Bridge above the dam, which gives the classic head-on view and avoids the queues entirely.