"A spaceship. The Super Nova is one of the largest in the known galaxy, and spherical in shape. We're in the center, and the Arboretum spans the entire diameter, give or take some space for barriers and service tunnels on the very outside, and I believe Mooj said this space would hold forty normal decks from floor to ceiling. It's the largest known man-made ecosystem in the galaxy, with old growth forests, mountains, rivers, and even a couple of sizable lakes."
He looked to Harry. "It's diameter is a little shorter in length than the United States from East to West Coast, maybe from about the middle of Nevada to the western edge of Virginia."