It's reported to be the largest treehouse in the world, and it's just off the interstate in Crossville, Tennessee. 

Visitors are invited to explore, at their own risk, free of charge.  And will find a true treat. 

This Crossvillian treehouse represents a case of Dr. Suess meets M.C.  Escher. I found myself wandering around in the labyrinth, alone, wondering where I was and hearing the trumpet sound of the rest of my family getting fainter and fainter as I continued my blind gropings.

I never could determine how many trees the edifice was built around, or perhaps it was only one giant tree, but I can guarantee you that trying to navigate via following the different trunks only gets you more lost.

I am 99% that it contains several nexuses to other dimensions with other Cumberland Counties in parallel universes; and I distinctly remember a "whisper-ma-phone" schlupping by while I was half the way up, although I never encountered the Lorax.  (Other's I passed in their tree-house pilgrimage assured me that he was indeed up there, but I did not see him personally).

But in a tree-house such as this, one never knows.

Besides many nooks and cranny's seats, a four story swing, and even a small chapel built in, there is the actual treehouse for which the edifice is known.

After much blundering around, I was able to scale the spiral "Staircase of Eternity" to the very top. 

At the top, I found what appeared to be a couple that looked human.  At this point, having already travel led to other several other parallel dimensions at lower stations of the tower, I decided to check first hand to see if they were indeed full-blown humans of the earthling persuasion.

I cleverly said a few words in "SnoK-tHorNk, the universal language of the Milky Way galaxy, "Snnflum;p grmpphaph!" 

(I spoke very fast to try to catch them off guard.)  The young lady looked at me blankly, and the young man politely said, "Bless you."

From this response, I immediately deduced that I had indeed portaled back into the "real" planet earth (Milky Way Galaxy) and was speaking with humans, so I quickly recovered by asking them if I could take their picture.  They politely agreed, and then requested that I also take one of them with their camera.

Amazingly, coming back down, the inter-galactic connect portals had transformed into knot holes on the tree and essentially were no longer visible to the untrained eye.

I made it down without incident, at which point I really wanted to go on one of the world's largest swings hanging from the 4th floor of the treehouse, but there were a number of grandchildren who wanted on first, so I abandoned my efforts and vowed to sneak back at some other, less populated time.

Note: I did receive a message to bring back to earthlings while I had been transmuted to the Zexflonian galaxy at Rigel 4, via a nexus in the tree house....that being "42."

All in all, it was an entertaining, unusual, and slightly mysterious earthbound portal of fun.