The Fortress of Doom (ディオスの神殿, Temple of Dios) known in later entries as Daos' Shrine, is a stronghold on Doom Island and the inner sanctum of the Sinistrals. In Lufia & the Fortress of Doom, it is where the party has to fight them.
In Lufia II: Rise of the Sinistrals, Daos uses the island as a last ditch effort at destruction by directing it toward Parcelyte. He leaves the scene, feeling sly. Without Selan to comfort him, Maxim beats himself up as if it was the end. Suddenly, Erim confronts Maxim one last time, but as Iris, to inform him that he can redirect the Fortress of Doom's path toward the bottom of the sea by destroying three Mystic Stones near the underside. However, destroying them meant killing himself in the process. She then conjures a portal to Doom Island's underside and leaves Maxim for good. Maxim destroys two of the Mystic Stones with no problem, but he was too weak to destroy the last one, so he mustered all reserve strength and drove it into the Dual Blade. With its energy combined with his, the final Mystic Stone is shattered....along with the Dual Blade. To save time, none of this was mentioned in the previous game, but it happened all the same.