Black Iron Palace

«Black Iron Castle» (黒鉄宮), alternatively translated as the Black Iron Palace, is a castle on the 1st Floor of Aincrad, located within the Starting City. It is the largest facility within the city and one of the most famous landmarks with Aincrad.

Description
The large rectangular black castle is located north of the Teleport Gate plaza of the Starting City and is encircled by large castle walls and a moat. The castle, assembled with black glossy pillars and metal boards, has a tall and large front gate, iron floors and an abnormally high ceiling. The air within the castle is significantly cooler than outside.

There is a Hidden Dungeon under the castle, likely to be unlocked by fulfilling a certain condition on the higher floors. It is also used as a headquarters and prison by The Army, usually for «Orange Players». Players violating the manner violation prevention code may be teleported to the Black Iron Castle's prison, if the victim chooses to confirm the system message warning them about the breach of ethics. Players can also be sent to the prison with the use of Corridor Crystals the destination of which is set for the prison.

Monuments
In the beta version of Sword Art Online, the castle housed the game's re-spawn point, called the Room of Resurrection. However, in the official version of the game, the Room of Resurrection was replaced by the Monument of Life, which kept track of the deaths of the SAO players. When Aincrad was later incorporated into New ALfheim Online, the Monument of Life was replaced with the Monument of Swordsmen, keeping track of the names of the participants of successful Labyrinth Boss raids. The monuments are placed in the hall right after entering through the main gate. Only this hall was open to the public at all times, while the deeper parts of the castle were in control of The Army during the official version of Sword Art Online.