6. Beach Rock Tree house



This treehouse by Japanese builder Kobayahsi Takashi was constructed with the express purpose of communicating with outer space. "A sparkling beacon among treetops, it is easy to imagine the dome succeeding at its mission to make contact with alien life," writes Nelson.

7. Island Wood Bogwon Tree house



The Island Wood "Bogwon" treehouse in Washington is supported by a single tree. Engineer Jake Jacob and his team from the TreeHouse Workshop fixed the house to the trunk with a series of limb-hugging rings. "Our trees are actually perched, as opposed to nailed in," he told us. "The tree might move in the wind and we don't want to inhibit the tree to be able to move in the wind."

8. 97-Foot Tree house



Horace Burgess's tree house may be as close to heaven as a body can get in Cumberland County. It rises 97 feet into the sky, the support provided by a live, 80-foot-tall white oak 12 feet in diameter at its base. Six other trees brace the tower-like fortress, but Burgess says its foundation is in God. Most of his materials are recycled pieces of lumber from garages, storage sheds and barns. The tree house has 10 floors, averaging nine to 11 feet in height by Burgess's reckoning. He has never measured its size but estimates it to be about 8,000 to 10,000 square feet. He did count the nails that he has hammered into the wood — 258,000, give or take a few hundred. And he guesses he has sunk about $12,000 into the project.

10. Crystal River Tree house



There is always a place for fun and frivolity in architecture! David Rasmussen, resident treehouse expert, designed and built this "treehouse" with log columns as the main support, since the trees on the property are not strong enough to build on.