Biosphere 2 is the world's largest closed-system glasshouse, an extraordinary three-acre complex of biomes built in the 1980s as an experiment in self-contained human habitation. There is an ocean (with coral reef), a rainforest, a savannah, a fog desert, and the agricultural and habitat zones — all under glass at the foot of the Santa Catalina Mountains north of Tucson.
Self-guided tours walk you through the biomes, the original habitat, the giant lung that compensated for thermal pressure changes, and the engineering corridors below. Plan a half-day. About 40 minutes' drive from central Tucson on the way to Oracle.