World’s Largest Treehouse

In 2005, the world’s largest all-wood treehouse was built amongst the lime trees of the non-profit Alnwick Garden in Northumberland County, UK. This 6,000 square foot treehouse is comprised of walkways, cottages, shops, a restaurant, and play areas. It is even wheelchair accessible, and holds close to 1,000 people, so everyone can play. - saynotocrack.com

Holy cow man! That's amazing... you gotta go check out the site and see the other pics. Wow...