At 710ft tall, Glen Canyon Dam is the nation’s highest concrete arch dam (the Hoover Dam, 16ft taller, is a different kind of structure). Forty-five-minute guided tours depart from the Carl Hayden Visitor Center and descend deep inside the dam via elevators. Exhibits tell the story of the dam’s construction (1956 to 1966), complete with all kinds of astounding technical facts. No backpacks or purses are allowed on the tour.