Dark, clear desert skies are the raison d'être for the Kitt Peak National Observatory, the world's largest collection of optical telescopes. Two radio telescopes and 22 optical telescopes sit atop a spectacular 6875ft-high mountaintop, offering stunning views across southern Arizona. The visitor center has exhibits and a gift shop, but no food. Hour-long tours take you inside the building housing the telescopes (alas, you can't peer through any of them) and the picnic area draws amateur astronomers at night.
For jaw-dropping views of the cosmos, sign up for the Nightly Observing Program, a four-hour stargazing session starting at sunset. It's limited to 46 people ($50; no programs from mid-July to the end of August because of monsoon season). The program books up weeks in advance but you can always check for cancellations when visiting. Dress warmly: it gets cold up here! A light dinner is included, and note that safety concerns preclude children younger than eight.
Kitt Peak is about 1¼ hours west of Tucson, along Hwy 86. There's no public transportation, but Adobe Shuttle runs 12-person vans from Tucson, starting at $275 one-way. It is cheaper to rent a car.