America's tallest national park monument, this graceful rainbow of shining steel soars 630 feet above downtown and the Mississippi River, commemorating westward expansion in the 1800s. Tram rides to the top (with great views on clear days) can involve lengthy waits in summer and on weekends; come first thing in the morning to purchase tickets (or order tickets in advance for an additional $3 fee online), then take in the Museum of Westward Expansion, which traces the journey of Lewis and Clark and those who followed. Extra fees are charged for both the Arch Odyssey Theatre, which features changing, 45-minute movies on a giant IMAX screen; and the Monument to the Dream film, documenting the Arch's construction. Plan on spending at least 2 hours here.