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 and attack players. 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
A Boss Room is an enormous room, located at the topmost floor of a Labyrinth in each Aincrad Floor. These rooms house doors to the stairs that lead to an upper Aincrad Floor, but these doors are protected by a powerful monster, called a boss, which requires large raiding parties to take down, that resides within the Room. After a boss is defeated, it will never re-spawn in the game.



The shape of the room differs from Floor to Floor. For example, the 1st Floor Boss Room was the shape of a rectangle, while the 74th Floor Boss Room was the shape of a dome. However, all Boss Rooms have several things in common. First of all, each one has only 2 entrances/exits: 1 from the Labyrinth below and 1 on the other side of the room leading to the next Floor. Although these doors usually stay open in SAO, allowing players to retreat from the Boss Fight if necessary, as the Bosses never leave their designated room, however, starting with the 75th Floor, the door would be sealed as soon as the players enter the room, preventing any chance of retreating. The Boss Rooms in New Aincrad are always sealed within 1 minute of entry, which is the time it takes for all the flames in the room to light up and form a circle and is considered as time given to players to prepare for the battle. The waiting time can be cancelled by pressing a stone button on the wall next to the door.

The Labyrinth-side entrance's appearance is usually a sign of the toughness of the boss inside: the lairs of weaker bosses usually have crude and rough entrances, while the lairs of powerful bosses are usually grim and made out of smoothly polished materials. All Boss Rooms are also quite dark, with many torches or other light sources, which only light up when the Boss Fight begins and dim out as soon as the battle is over, spread out throughout the room. Boss rooms starting with the 74th Floor come with Anti-crystal fields, which prevent the use of any crystals, including teleportation crystals, within the Room.

However, not all Floor Bosses in Aincrad have actual Boss Rooms. The Boss of the 56th Floor was a field type boss guarding the entrance to the 57th Floor in a field next to a town, instead of within a Labyrinth.

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

 * Sunshine Forest (20th Floor)
 * The «Forest of Wandering» (35th Floor)
 * Ant Hill (46th Floor)
 * The «Hill of Memories» (47th Floor)
 * Hidden Dungeon (a hidden dungeon under the Black Iron Castle)

ALfheim Online

 * Jötunheimr.
 * Þrymheimr (the Inverted Ice Pyramid in Jötunheimr).
 * The North, East, South, and West dungeons of Aarun city.