Biosphere 2 is located in the Arizona desert near Tucson. I've been there, and it's a fascinating place—a massive research facility initially designed to model a closed habitat (of great interest if we plan to colonize Mars or the moon), that is now given over to all kinds of research projects (some of them even space-related).
Although the initial Biosphere 2 experiments ended in very public mishaps, the ambition and scale of the place is still stunning. It's still standing, now owned and maintained by the University of Arizona. You can take a tour...or you can watch the video below, in which Craig Benzine gets an excellent tour of the facility, even getting to stand on the beach. (Public tours typically just walk past it on a walkway.) Yes, there's a beach, and a mini-ocean. That's just one of the various biomes within the enclosed biosphere.
When I visited circa 2008, the most fascinating part of the tour was the so-called "technosphere," the area below ground housing machinery that maintains the system—it's a giant basement crammed with enormous HVAC units, water management tech, and other gear. Within the technosphere, the freakiest part is The Lung. Without ruining it, let's just say that Benzine does get to visit and interact with The Lung in the video below. That thing is 25-ish years old, and it's still "breathing."
If you've ever wondered what Biosphere 2 is, what it's doing lately, or the kinds of research scientists can do with a giant enclosed system, this is the best it gets. Enjoy:
See also: Two Years in Biosphere 2.