Tree of Knowledge

The Tree of Knowledge is a 5,000 year old gigantic library tree surrounded by houses. It is located on Ohara island, which is currently a burnt land and was also Robin's homeland. The tree was used by archaeologists who were able to decipher the poneglyphs. As research of Poneglyphs are forbidden by the World Government they sent CP9 to attack the archeologists and called forth the buster call. When Spandine the chief of CP9 back then activited Buster Call to destroy Ohara, the tree fell and crushed almost every historian. It is here where Nico Robin learned to read this language, unbeknownst to the professors. Its library was the oldest known structure in the One Piece world.