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. When the World Government sent a Buster Call to destroy Ohara, the tree fell and crushed almost every historian. The tree was used by archaeologists who were able to decipher the poneglyphs. 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.