???/Mysterious Island (Outer Sea)

Overview
This location just appears as ??? when Luka enters it. A monument is located at the center of the island, and talk about "children abducted by a circus troop on Degris Hill" before most (but not all) bones were found later. This place can only be accessed after exploring the other mysterious island, and the tombstone only updates itself after dealing with the Cirque du Croix, confirming the link between the three.

Trivia

 * The BGM playing in the area is dungeon_labo 1 (which is used in the Administrator Tower and the laboratory under Remina in the original storyline), making it safe to assume that the place will be related to the barely touched Alliance of Wisdom.