Cairos Dungeon is a collection of dungeons which includes the five elemental halls and the Hall of Magic, the Giant's Keep, the Dragon's Lair, the Necropolis, and occasionally the Secret Dungeons, Hall of Heroes, Angel Garden, Rainbow Garden and Devilmon Cave which are only available at limited times. Access to this area is granted to players after completing Kabir Ruins.
Each of the dungeons usually require the player to advance through waves and defeat a boss in order to clear it. Though each dungeons have specific victory rewards, defeating monsters in any dungeon will award Experience Points and sometimes Mana Stones, Energy and Crystals.
The Halls of Elements includes five dungeons: the Hall of Dark, Hall of Fire, Hall of Water, Hall of Wind, and Hall of Light. Each dungeon contains ten floors consisting of three waves each in which players must defeat a boss at the third wave to clear it. Doing so often awards players with special elemental Essences specific to the element of the dungeon. These essences are required to awaken monsters. Additionally, players may also find an Angelmon belonging to the element of the dungeon in which they are found.
Each boss in the dungeons is aided by two crystals which provide buffs for the boss, and debuffs against players. The bosses themselves each possess different abilities depending on the floor and element, although they generally get stronger as the floor number gets higher.
Usually, each dungeon is open only on the day of the week when the dungeon's element corresponds to the Classical Chinese name for the day of the week. Once a dungeon closes, players must usually wait until the following week. As an exception, monthly events open all five dungeons for three days, Friday through Sunday.
| Day | Hall | Essence |
| Sunday | Hall of Light | Essence of Light |
| Monday | Hall of Dark | Essence of Dark |
| Tuesday | Hall of Fire | Essence of Fire |
| Wednesday | Hall of Water | Essence of Water |
| Thursday | Hall of Wind | Essence of Wind |
The Hall of Magic is similar to the five different elemental dungeons in that ten floors are available, with essences often awarded for clearing a floor. The essences unique to the Hall of Magic are the Essences of Magic, although essences for the of Magic is always open. Bosses here are similar to the Halls of Elements, in that two crystals aid the boss with buffs,debuffs against players. As the floor number gets higher, the bosses general gets stronger in each stage
The Giant's Keep contains twelve floors, each of which requires defeating a Water element Ancient Giant as a boss. Doing so awards players with Runes. This location is the primary source of Despair Runes. Other possible rune drops are Energy, Fatal, Blade, and Swift. Like the Halls of Elements and Hall of Magic, two crystals aid the Giants here. As well, the Giants possess the unique ability to counter attack every 7th attack from your monsters.
The Dragon's Lair contains twelve floors, each of which requires defeating a Fire element Legendary Dragon as a boss. Doing so awards players with Runes. This location is the primary source of Violent Runes. Other possible rune drops are Revenge, Endure, Focus, Shield and Guard. Like the Halls of Elements and Hall of Magic, two crystals aid the Dragons here. As well, the Dragons possess the unique ability to counter attack when a crystal is destroyed.
The Necropolis contains twelve floors, each of which requires defeating a Dark Element Ancient Lich King as a boss. Doing so awards players with Runes. This location is the primary source of Rage Runes. Other possible rune drops are Vampire, Nemesis, Will, and Destroy.
The Steel Fortress contains ten floors, each of which requires defeating a Wind Element Ancient Tormenter as a boss. Doing so awards players with Artifacts. This location is the primary source of Attribute Artifacts.
The Punisher's Crypt contains ten floors, each of which requires defeating a Light Element Ancient Punisher as a boss. Doing so awards players with Artifacts. This location is the primary source of Type Artifacts.
Secret Dungeons are special dungeons in which players advance through ten waves, with each wave requiring players to defeat a large number of the same monster to advance. Advancing through the waves awards players with special summoning pieces which can be used to summon the monster encountered in the dungeon. The number of pieces awarded depends on the number of waves cleared. Secret dungeons are usually only available as a random encounter in the Halls of Elements, although they are sometimes made available as a special event for all players. Usually, only 2-star and 3-star monsters are found here.
The Hall of Heroes is similar in that players receive special summoning pieces for clearing an entire floor. There are 10 floors available here, however each floor can only be completed once, and each floor contains six waves. There is a mini boss on the third wave, and three bosses on the sixth wave. On the sixth wave there is the main boss, the same unit that you will get summoning pieces for, and two mini bosses of different attributes from the same family. There are 25 pieces awarded for clearing each floor, and summoning a 4-Star monster costs 50 summoning pieces. As only 4-star monsters are available here, clearing the dungeon is generally quite difficult, especially for newer players. The Hall of Heroes is only available once a month as a special event for all players.
The Angel Garden is a special dungeon in which players are awarded an Angelmon of a specific element and level for clearing a floor. Three floors are available, with each floor requiring players to defeat a giant sized Angelmon to clear it. Since the Angelmon divides repeatedly every time it is defeated, players must defeat it multiple times to clear the floor. The garden is only available once a month as a special event for all players. During that event, dungeons for the elements Fire, Water, and Wind are open during a scheduled window of time.
The Rainbow Garden is a special dungeon in which players are awarded a Rainbowmon of a fixed grade or star rating for clearing a floor. Only one floor is available, with players requiring to battle against a giant sized Rainbowmon to clear the floor. Like the Angel Garden, the boss divides repeatedly every time it is defeated, requiring players to defeat it several times to clear the floor. The garden is only open once a month as a special event for all players, and may not be repeated once cleared.
The Devilmon Cave is a special dungeon in which players are awarded a Devilmon for clearing a floor. Only one floor is available, with players requiring to battle against a giant sized Devilmon to clear the floor. Like the Angel Garden, the boss divides repeatedly every time it is defeated, requiring players to defeat it several times to clear the floor. The cave is only open once a month as a special event for all players, and may not be repeated once cleared.
| Language | Title |
|---|---|
| English | Cairos Dungeon |
| Korean | 카이로스 던전 |
| Japanese | カイロスダンジョン |
| Traditional Chinese | 卡伊洛斯地下城 |
| Simplified Chinese | 卡伊洛斯地下城 |
| French | Donjon de Cairos |
| German | Cairos-Dungeon |
| Russian | Подземелье Кайрос |
| Portuguese | Masmorra de Cairos |
| Spanish | Mazmorra de Cairos |
| Indonesian | Cairos Dungeon |
| Malay | Penjara Bawah Tanah Cairos |
| Vietnamese | Hầm Ngục Cairos |
| Thai | ดันเจี้ยนไครอส |
