The Mission San Xavier del Bac sits in the desert outside of Tucson, on the Tohono O'odham Nation San Xavier Indian Reservation. It was constructed in the late 18th century (1783-1979) after its previous incarnation was destroyed in an Apache raid. It is an absolutely beautiful example of Spanish architecture in the American southwest. Franciscan friars still live at the mission, and it is still a pilgrimage site for the faithful. Highly recommended visit.