I googled but cannot find any information regarding this new area. I believe it is only available after a new game plus. Has anyone found it? So at the bottom of the Sea Prison, there is a door to another area. I do not remember seeing the symbol before completing the game. This secret area has 4 level and 12 chests. There are two challenges. Both are fighting challenge. There is a Kizaru that will give 90 skill point per kill. There is a robot assembly factory area and there is a robot with two swords that looks like Zoro. Too bad you can't fight it.