Treehouse expert and visionary Pete Nelson explores the evolution of treehouses through delving into the many shapes and vast variety of functions they've served throughout the years. “Ultimate Treehouses 2” features a Papua, New Guinea, high-in-the-sky tribal treehouse built by hand, the world’s oldest backyard treehouse (more than 200 years old), a luxury treehouse gem in New York and a re-purposed airplane fuselage in Costa Rica. The special also spotlights fully suspended biospheres in the wild skies of British Columbia. Follow Pete’s jaw-dropping journey into the past, present and future of treehouse design.