Biosphere 2 in Oracle, Ariz., is a spaceship-like glass facility, elevated on a ridge nearly 4,000 feet above sea level at the base of the Santa Catalina Mountains. You can learn about the past and future of our planet there, and be sure to visit the Phoenix Mars Lander exhibit, which holds the spacecraft that landed on Mars in 2008. TIME-LIFE Books named the site — a scenic drive north of Tucson — one of the 50 "wonders of the world."