Built to be completely sealed off from Biosphere 1 (the earth), Biosphere 2 is 3 acres of glass domes and pyramids containing six ecosystems: ocean, mangrove, rainforest, savannah, desert and city. In 1991 eight biospherians were sealed inside for a two-year tour of duty, from which they emerged thinner but in fair shape. Tours take in the biospherians' apartments, farm area and kitchen, the million-gallon 'tropical ocean' and the 'technosphere' that made it all possible.
Although this experiment was ostensibly a prototype for self-sustaining space colonies, the privately funded endeavor was engulfed in controversy. Heavy criticism came after the dome leaked gases and was opened to allow a biospherian to emerge for medical treatment. After several changes in ownership, the sci-fi-esque site is now a University of Arizona–run earth-science research institute.
Biosphere 2 is near Oracle, about 30 miles north of Tucson via Hwy 77 (Oracle Rd) or 30 miles east of I-10 (exit 240, east on Tangerine Rd, then north on Hwy 77). Unfortunately it's not wheelchair (or stroller) accessible.