You won't have to search the ocean or a subterranean dungeon for this treasure -- Atlus announced that copies of Etrian Odyssey 3: The Drowned City pre-ordered from certain retailers will include "Forests of Eternity," a 60-page artbook. The full-color book includes character and background artwork not only from The Drowned City, but from the previous Etrian Odysseys as well.
But why tell you about it when we can show you? Atlus posted an excerpt of the book for you to page through. "Beware!" it notes. "The artwork and designs contained in this book may reveal more than you wish to know of Etrian Odyssey III!" You'd be better off avoiding the preview, then, if you've got a spoiler allergy.