Raftel, the final island?
Yeah, that's "hidden".. I mean, Skypiea was totally hidden, but the Straw Hats found it due to searching for the Legend and then meeting up with Masira and the Monkey Crew; they might just stumble over a possible Raftel Legend later on....
... here's an awesome OP pic I found~!!
http://izouvou.onigiri.free.fr/pictu...roOda/gros.jpg
Captures Monkey D. Luffy's personality straight on. I'd rate it 8.4/10.