Located in Crossville, Tennessee, this treehouse took Horace Burgess 14 years to build it around an 80-foot-tall white oak tree, with a diameter of 12 feet. Six other strong trees that act like natural pillars support the 97-feet-tall wooden edifice. Burgess started working on this huge treehouse after he had a vision back in 1993. The treehouse has 10 floors, averaging 9 to 11 feet in height with an estimated 8,000 to 10,000 square feet. This 56-year-old landscape architect used about 258,000 nails in this structure and $12,000 to construct it.