A much more modern and adaptable tree house design, the O2 structures are as green as they come: “based … on Fuller’s geodesic sphere [with] covering options made from 100% hemp canvas, recycled milk carton plastic and 60% post-consumer waste eco-resin. The result is a translucent sphere that glows softly when lit from within.” Because these are suspended from cables and easy to assemble and dismantle they have very little negative impact on their environments. (Source)