The Inverted Castle (逆城都市) is a Legendary Land located at Θ Bitter Fantasy Mirror World. It appears as an upside-down floating castle composed of countless stone spires. The Castle is visible from numerous fields throughout Theta Server.
The World Storyline
No one knows this castle's real name, and the inhabitants all seem to have disappeared ages ago.
Believing that the Castle was the hiding place of the legendary Key of the Twilight, several characters entered the castle in search of it. Following clues from the BBS the players BT, Crim and Sora succeeded in entering the Castle via the Twilight Eye located at the Hulle Granz Cathedral. Tsukasa, along with Mimiru and Bear also managed to enter the area, using Tsukasa's ability to teleport throughout The World. All of the players scrambled to reach the center of the area, believing that the Key was there. BT was the first to reach the center, and discovered that it was not the Key that resided in the castle, but an AI copy of Harald Hoerwick. Tsukasa arrive shortly afterwards, and also met with the AI. Through his conversation with Harald Tsukasa realized what and where the Key actually was. Unfortunately he was attacked by Macha upon leaving, and had all memories of the encounter erased by Macha's Data Drain.
Later Bear, Mimiru, and Subaru returned to the Castle, using a portal created by Helba. They met again with Harald, and learned more about his daughter Aura. However their visit also alerted Morganna to the AI's existence, and she used her power to eliminate him from the system.
The Inverted Castle was a bonus dungeon in .hack//MUTATION. Kite and several party members traveled to a platform in the center of the city, where they battled against the ferocious Angolmore. After a long and grueling battle, Kite succeeded in defeating the creature. As a reward he received the rare item Crimson Raid.