This national historic landmark was built in 1894 by Percival Lowell. The observatory has witnessed many important discoveries, the most famous of which was the first sighting of Pluto – in 1930 through the 1896 24-inch Clark Telescope. In the '60s NASA used the Clark telescope to map the moon. Weather permitting, visitors can stargaze through the telescope; check the website for the evening schedule. The short, paved Pluto Walk climbs through a scale model of our solar system, providing descriptions of each planet. You can stroll the grounds and museum on your own, but the only way to see the telescopes and lovely observatories is on a tour (on the hour from 10am to 4pm in summer; on the hour from 1pm to 4pm in winter).