In the series finale, "Come Along With Me," the original Tree House was destroyed by a monster summoned by GOLB. Following the battle, Fern (the Grass Finn) passed away and left behind a small seedling shaped like the Finn Sword.
An abandoned jail cell, a demon-summoning vault, and even an entire civilization living within the walls. Destruction and Rebirth Adventure Time Tree House (Tree Fort)
Finn and Jake planted this seedling where their old home once stood. A thousand years into the future, that seed grew into a gargantuan tree that towered over the Land of Ooo, serving as a new landmark for the next generation of heroes, Shermy and Beth. In the series finale, "Come Along With Me,"