Tucson, AZ: Biosphere2. See GALLERY. This is a very impressive complex to tour. The entire place is hermetically sealed, unlike green houses at a typical botanic garden. There were tropical zones as well as desert zones all climate controlled. In order to prevent the glass from exploding due to air pressure changes during the day there were two “lungs” that would expand and contract as the pressure varied. Each “lung” was 150′ across with a ceiling weighing a few tons would rise and fall as needed. Originally the Biosphere hosted a number of scientists who were sealed into the facility for a couple of years to study self-sustaining environments. There are currently no residents housed there but various experiments are still on going.