In a small desert town about an hour outside Tucson lies one of the most fascinating science experiments ever created. Biosphere 2 is the largest closed ecosystem in the world, and scientists have been studying the interactions between life systems and people there for nearly 20 years. It's essentially an enormous, sealed greenhouse that contains man-made versions of the earth's different climate and geographic zones, including a rainforest, an ocean with a coral reef, mangrove wetlands, savanna grasslands, a desert, a farm, and human habitat. As for the humans, two experiments were conducted in the early 1990's in which groups of people entered the sealed biosphere and stayed for extended periods of time. While the experiments revealed plenty of fascinating environmental data, they also showed that people don't always get along when locked into a confined space together. Fortunately, visitors to this scientific masterpiece don't have to worry about getting locked in, so they can just relax and enjoy the guided tour through the different ecosystems. The rainforest (pictured), with plants that reach up to 60 feet in the air, is stunning, particularly when you consider just how unlikely it is to have such a lush, humid forest in the middle of the desert. Starwood has three hotels in Tucson, including the Sheraton Tucson Hotel & Suites.