TreePods
Weburbanist has a great post detailing 10 amazing tree houses, including Free Spirit Spheres

and “grow your own” varieties. These latter, from a combination of scaffolding and other systems, could be used to direct the growth of concept tree houses over a period of years. Vines, roots and trees become organic architectural materials to create a flexible framework. Windows would be made of flexible soy membranes that would shift as the building grew.

Well worth checking out the full post for some real tree hugging fun.

Deeply reminiscent of that one level in Myst.
I’m consistently surprised that when such concepts are discussed, especially with that last one, that nobody mentions Paul Laffoley’s Das Urpflanze Haus. Yes, he’s a mad old kook; that doesn’t mean he isn’t on the money.