In just 15 miles south of San Xavier, you can travel from the colonial 1700s to the Cold War 1960s by stopping at the Titan Missile Museum, the only Intercontinental Ballistic Missile (ICBM) silo preserved intact and open to the public anywhere in the world. On the north side of the sprawling stucco retirement community of Green Valley (pop. 17,283), just west from I-19 off exit 69 on Duval Mine Road, the silo was in active use from 1963 until 1982, was declared a National Historic Landmark in 1994, and is now open for tours (daily; $8.50; 520/625-7736). The tours, which take around an hour, involve donning a hard hat and descending stairs into the control room of the hardened silo, which still contains a 110-foot-tall Titan missile.