The Sooper Double Mega Triple Treehouse was the biggest and greatest treehouse ever seen on Earth. It was built in ancient times for kids by adults, who later destroyed it.
Numbuh 1 mentioned it in a school report while presenting the origin of adults.
In the ancient times, not long after kids created adults, they ordered the adults to build for the coolest monument yet; a grand treehouse larger than any treehouse built before it. It would be big enough for all the world's kids to live and play in. The construction of the treehouse put such a strain on the adults, that one grownup snapped; Mr. Wigglestein. He spanked a child, resulting in a trial where it was decided to ban all adults from the treehouses. A war started between the kids and the adults, which culminated in the adults charging with an army at the grand treehouse and chopping it down; forcing the kids to evacuate to the Moon (Operation: A.R.C.H.I.V.E.)-
- Due to Numbuh 1's nature of exaggerating, it's not known if this treehouse did indeed exist.