Rising 867 feet from its base, Devils Tower in Wyoming is the first National Monument. The tower is made up of mostly hexagonal columns, but some have as few as four or as many as seven sides. In 1906 President Theodore Roosevelt proclaimed Devils Tower the first national monument under the new Antiquities Act, thus protecting it from commercial exploitation.
Climbing the Tower is allowed. If you look closely at the photograph near the top center, you can see the climber.