Inside the Ruins is simply the title applied to just that: The inside of Marige Atoll. The inside of the ruins consists of a maze of rooms and hallways including a pair of ancient mechanisms that make several passages one-way journeys.
In the western area of the ruins in Marige Atoll, there is a mazelike area of large, rectangular pillars. In this maze, one of the entrances to the internal ruins can be found. The first large room inside the ruins is the Room of Oracles, and after that is a string of rooms leading to the final room, known as the Prince's Room.
Another entrance to the ruins, after unlocking it, is a hole in the ceiling of the room at G-7, the room which contains two Atlantic Tarpon and a single Marbled Ray. The third and final entrance is to the very south of the ruins, leading into the same room with the hole in the ceiling.
Inside the ruins are multiple Stone Monuments, engraved with mysterious writing. As well as these monuments, there are a pair of treasures that are scattered about the ruins: the Deity Idol and the Inscribed Nephrite.