Not to be confused with the hidden dungeon that appeared in the series' game adaption.

The Hidden Dungeon (隠しダンジョン, Kakushi Danjon?) is a dungeon that is hidden beneath the Black Iron Palace.


Hidden Dungeon Entrance

Entrance into the Hidden Dungeon.

The entrance to this dungeon is located outside the Black Iron Palace and, accessed through an underground water supply. The dungeon has a notably high level difficulty, despite being on the 1st Floor. The dungeon's walls are made of black stones and lined with columns. A safe area lies at the end of this dungeon, which is guarded by The Fatal Scythe.

The Safe Area is a completely white room with smooth walls and floor. A black cube, a Game Master (GM) console, is placed in the middle of the room.

When the boss appears, the surrounding area turns into a shade of violet blue, and some of the stone walls are given a new graphic as well.

Hidden Dungeon Corridor Boss

Appearance of the dungeon after appearance of The Fatal Scythe.

Notable LocationsEdit

  • Safe Area
  • The Fatal Scythe's Boss Corridor


Aincrad ArcEdit

Morning Dew GirlEdit

Kibaou used this dungeon to trap Thinker when the latter was considering of discharging him from the guild for getting his men killed by The Gleam Eyes on the 74th Floor. Thinker was trapped for three days until Yulier finds Kirito and Asuna to help her. Yui demanded to come along as well, and the group reluctantly agreed.

Kirito easily sliced through the dungeon’s monsters and they soon saw the safe area where Thinker was being held. Yulier ran towards the safe area, and Kirito barely managed to knock Yulier aside to prevent her from being hit by The Fatal Scythe. Kirito prompted Yulier to retreat to the safe area with Yui as he confronted the boss. Seeing that the boss has too high of a level to identify, Kirito soon told Asuna to leave as well. Asuna disagreed and fights alongside Kirito. The Fatal Scythe knocked both high-leveled players down, taking away about half of their HP along with it.

Yui steps out from the safe area as Thinker and Yulier teleport away. The Fatal Scythe detects Yui and attacks her, but is stopped by her «Immortal Object» status. Yui then uses the GM console's «Object Eraser» function, in the form of a large sword, and easily defeats the boss. She then turns to her "parents" and tells them that she remembered everything.

In the safe area, Yui explains that she regained her memories after touching the GM console when Yulier first brought her inside. Yui also says that she wishes to be with them forever, but will be shortly deleted from the system as a foreign object. Kirito intervenes and uses the still-active Admin access and his computer skills to retrieve Yui and save her as an in-game item, «Yui’s Heart», as part of his NerveGear’s environment data.

Known MonstersEdit

Known BossesEdit



  • The dungeon was not available in the beta version of Sword Art Online.
  • The dungeon only becomes accessible after a certain condition on the higher floors is fulfilled.



Aincrad Locations Navigation Bar
Teleport Gate
Floor Notable locations and landmarks
1 Town of BeginningsBlack Iron Palace, Hidden DungeonMonument of Swordsmen[Navbar 1]Monument of Life[Navbar 2]Chamber of Resurrection[Navbar 3]TolbanaHorunka Village, Medai Village
2 Urbus, Urbus Teleport Gate Plaza, Marome Village, Taran Village
3 Forest of Wavering Mists, Zumfut, Zumfut Teleport Gate Plaza, Dessel
4 Rovia, Rovia Teleport Gate Plaza, Bear Forest, Yofel Castle, Usco Village, Caldera Lake
5 Karluin, Karluin Teleport Gate Plaza, Mananarena, Shiyaya
6 Stachion, Stachion Teleport Gate Plaza, Suribus, Ararro, Castle Galey, Lake Talpha
7 Monster Arena[Navbar 4]
8 Frieven Village, Frieven Teleport Gate Plaza
9 Dark Elf Queen's Castle[Navbar 5]
10 Thousand Snake Castle[Navbar 6]
11 Taft, Taft Teleport Gate
19 Ralberg, Ralberg Teleport Gate, Hill of the Cross, Griselda's Tomb
20 Sunshine Forest
22 Coral Village, Coral Teleport Gate Plaza, Forest House K4, Lake Outside Coral Village
24 Panareze, Panareze Teleport Gate Plaza
25 Giltstein, Giltstein Teleport Gate Plaza, Former location of the Knights of Blood Headquarters
27 Ronbaru Town, Ronbaru Teleport Gate
28 Wolf Plains
35 Forest of WanderingMishe, Mishe Teleport Gate Plaza
39 Nolfret, Nolfret Teleport Gate Plaza, Former location of the Knights of Blood Headquarters
40 Jaileum, Jaileum Teleport Gate Plaza
46 Ant Hill
47 Floria, Floria Gate Plaza, Hill of Memories, Forest of Giant Flowers
48 Lindarth, Lindarth Teleport Gate Plaza
49 Myujen, Myujen Teleport Gate Plaza
50 Algade, Algade Teleport Gate Plaza
55 Granzam, Granzam Teleport Gate Plaza, Knights of Blood Headquarters, West Mountain
56 Pani, Divine Dragon Alliance Headquarters
57 Marten, Marten Teleport Gate Plaza
59 Danac, Danac Teleport Gate Plaza
61 Selmburg, Selmburg Teleport Gate Plaza
65 Old Castle Labyrinth
66 Old Castle Labyrinth
72 Ozmalt, Ozmalt Teleport Gate Plaza, Agarla Village
74 Kamdet, Kamdet Teleport Gate Plaza
75 Collinia, Collinia Teleport Gate Plaza
100 Ruby Palace
  1. Only in New ALO
  2. Only in the SAO official service
  3. Only in the SAO Beta
  4. According to Kirito in Progressive Volume 1, Rondo of a Fragile Blade, Part 1
  5. According to Kizmel in Progressive Volume 3, Barcarolle of Froth, Part 7
  6. According to Kirito in Progressive Volume 1, Aria of a Starless Night, Part 14
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