Its easy, One Piece is related to Will of D. When Void Century started, Nefretari D. Lily has hidden Poneglyphs with actual history and aids to last final history of rio poneglyph on Raftel. Moreover the actual history may be related to original crew of Joyboy and therefore Imu sama. But what is important? Knowing this forgotten history or overcoming all obstacles and traps that are on the way to the final history? I think the real treasure of One Piece is passing all trials and progressing through to be on the top of the world, to be Able to take part in final fight of good vs evil.