Biosphere 2 is a huge glass-and-steel earth science facility built to hold sealed replicas of major ecosystems: rainforest, ocean, mangrove wetland, savanna, desert, and experimental research spaces. Its original closed-system missions made it famous; today the University of Arizona uses it for climate, water, and ecosystem research.
The guided visitor route is the reason to go. You see the scale of the structure, the artificial biomes, and the service spaces that made the experiment possible. It is odd, ambitious, and still fascinating even if you are not usually drawn to science museums.