After much discussion back in the late 1950s, tribal leaders of the Tohono O'odham nation agreed to share a small section of their 4,400-square-mile reservation with the National Science Foundation to house sophisticated research telescopes. Among these is the McMath-Pierce, the world's largest solar telescope, which uses piped-in liquid coolant. From the visitors' gallery you can see into the telescope's light-path tunnel, which goes down hundreds of feet into the mountain.
The visitor center has exhibits on astronomy, information about the telescopes, and hour-long guided tours ($7.75 per person) that depart daily at 10, 11:30, and 1:30. Complimentary brochures enable you to take self-guided tours of the grounds, and there are picnic areas outside and below the observatory. The observatory sells snacks and drinks, which is good to know, because there are no restaurants (or gas stations, for that matter) within 20 miles of Kitt Peak. The observatory offers an outstanding nightly observing program ($49 per person); reservations are necessary.