Lowell Observatory sits on Mars Hill, a low ridge above downtown Flagstaff, and has been one of the most productive astronomical research institutions in the United States since Percival Lowell established it in 1894. Lowell himself was primarily interested in Mars — convinced it harbored an intelligent civilization — and spent years mapping what he believed were canals. He was wrong about the canals but right that Flagstaff's high altitude and clear, dark skies made it ideal for astronomy.
The observatory is open to the public for daytime and evening programs. The historic 24-inch Alvan Clark refracting telescope, through which Pluto was discovered, is still operational and visitors can look through it on clear nights. The Steele Visitor Center has exhibits on the history of the observatory and the solar system. This is one of the more engaging science attractions in Arizona, particularly for anyone with children interested in space.