They found it as an old treehouse. They fixed it up some, and elaborated on it. They're essentially squatters, although was was just an abandoned, unowned treehouse. There are whole sections where they've replaced or reinforced the wood, and some areas are all new. There are extension cords running through the whole thing now, and a hose runs up to the lower level. Currently dwelling there is Alexandria Raintree, Cressida Allen, Kitrino Perro, and Chanterelle Lombric-Argenta.
There's really nothing to call it but, "Umm... you know... that place we all live..."