PHOENIX A saguaro cactus is seen at twilight against the city lights. This desert metropolis hosts two of the 10 largest city parks in the country: South Mountain Preserve and North Mountain Preserve. While Phoenix also boasts plenty of traditional parks with ball fields and playgrounds, the preserves feature "pristine Sonoran desert in its natural state," says Ken Vonderscher, the city's deputy director of parks and development. South Mountain Preserve alone contains 51 miles of trails for hiking, biking, and horseback riding.