Dungeon

A Dungeon is any type of adventuring location in an MMO, which is designed like a labyrinth or maze-like structure that has numerous paths, monsters, and rooms (for closed dungeons). Two main types of dungeons exist in Sword Art Online, labyrinths and sub-dungeons.

In Aincrad, labyrinths are tower-like structures with many floors that connect each Aincrad Floor to the next and are found on every floor. The Boss Room of a labyrinth must be found on the topmost labyrinth level and cleared before the stairs to the next Aincrad Floor are opened.

Another type of dungeon that exists in the SAO universe is called a sub-dungeon in SAO or just dungeon in other games. In Aincrad, these dungeons are not important to the clearing of the game, so Clearers do not take the time to clear them, therefore, they are mainly cleared by middle level players. This type of dungeon also exists in Alfheim Online and is the main type of dungeon in the game until New Aincrad is implemented into the ALO universe. This type of dungeon also exists in other VRMMOs. For example, there is a huge ruins dungeon beneath SBC Gurokken in Gun Gale Online.

Strategy
Labyrinths in Sword Art Online are literally mazes, full of difficult winding paths, traps, hidden rooms, and dead ends. Because of the difficulty of the paths, it often takes Front Line players a week to "map" the labyrinth on average, before the Boss Room is found.

At that point, Front Line players typically hold a meeting to strategize the Boss Battle. Several expeditionary parties are sent to gather information on the Boss before a real raid is attempted.

Between the Closed Beta Test and the Official Release, the labyrinth maps were likely changed, since it took more than a month for the first floor Boss Room to be located.

Safe Areas
Most dungeons have a handful of safe areas, where monsters do not enter. They can be recognized by a special colored torch placed in the four corners on the wall. Although it is possible to stay in safe areas for several days on end, it is described as a particularly discomforting and sleepless experience, since nearby monster footsteps or growls can be heard frequently.



Boss Rooms
Every labyrinth has a boss room. It is usually seen as a large, enormous door set against a wall or dead-end. In the poor-lighting in most dungeons, only by entering do the rooms lit up completely, they are often difficult to make out otherwise. Bosses normally never leave their Boss Rooms. After a boss is defeated once, it will never re-spawn in the game.

Anti-Crystal Field
One of the most lethal (but rare) traps in Aincrad's labyrinths is the Anti-Crystal Field trap. It gives off a red color that prevents the usage of any crystals, including teleport crystals. As a result, players who enter anti-crystal field rooms are forced to defeat all enemies or face death. Beginning with the 74th Floor, Boss Rooms also became anti-crystal fields.

Sword Art Online

 * The «Forest of Wandering»
 * The «Hill of Memories»
 * The Black Iron Castle dungeon (a hidden dungeon under the Black Iron Castle)

ALfheim Online

 * Jötunheimr
 * The North, East, South and West dungeons of Aarun city