Tucson

Tucson needs 1 day: touring Saguaro National Park, split into two sections on either side of the city, with forests of the saguaro cactus that only grows in the Sonoran Desert, and visiting the Arizona-Sonora Desert Museum, a hybrid outdoor zoo, botanical garden and natural history museum, the same afternoon. October-April avoids the extreme desert heat. It's cheaper than Phoenix or Scottsdale. It's Arizona's second most populous city and home to the University of Arizona, and its sky -protected by light pollution ordinances since the 1970s- made it one of the world's astronomy capitals, with several of the planet's most important observatories in the nearby mountains.