Aincrad

 Aincrad (アインクラッド) is the first « Realized World » shown in the « Sword Art Online » light novel series. It's full name is An Incarnating Radius (アン・インカーネイティング・ラディウス).

Background
Aincrad is the world set as the stage for « Sword Art Online », declared as the world's first in VRMMORPG genre. It was incorporated in «ALfheim Online» on May 2025.

The base currency of Aincrad is the Col.

Etymology and Meaning
A «Realized World» called "An Incarnating Radius;" the name has been abbreviated as Aincrad. It is also inferable that its design is symbolic for time and space. the vertical axis representing time and the circular floors representing space.

Geography
Aincrad is an iron-and-stone made floating castle that has about 10 kilometers floor base diameter and consists of a 100 floors stacking straight upwards, meaning that each floor's diameter is a bit smaller than the previous one. Each floor, there are a couple of large cities along with countless small scale towns and villages, forests, plains, and even lakes. Only one stairway links each floor to another, and the stairways exists beyond the boss room of each dungeons. The «Teleport Gates» of every unlocked cities are connected to one another.

Known Bosses

 * Illfang the Kobold Lord (Boss Monster of the 1st Floor)
 * Baran the General Taurus (Boss Monster of the 2nd Floor)
 * Two Headed Giant (Boss Monster of the 25th Floor)
 * Ant Queen (Boss Monster of the 46th Floor)
 * Six-Armed Metalic Statue Buddah (Boss Monster of the 50th Floor)
 * The Geocrawler (Boss Monster of the 56th Floor)
 * The Gleam Eyes (Boss Monster of the 74th Floor)
 * The Skull Reaper (Boss Monster of the 75th Floor)
 * Heathcliff (Supposedly Boss of the 100th Floor)
 * Nicholas the Renegade (Boss Monster of the Lost Forest in Christmas Event)
 * The Fatal-Scythe (Boss Monster of the Black Iron Castle Hidden Bonus Dungeon)

Known Monsters

 * Blue Slug
 * Dark Elf
 * Demonic Servant
 * Drunken Ape
 * Dusk Lizard
 * Elder Treant
 * Feathery Dragon (Pina)
 * Flower Monster
 * Walking Flower
 * Forest Elf
 * Four Eyed Frog
 * Frenzy Boar (Level 1)
 * Frost Dragon
 * Gargoyle
 * Giant Venus Fly Trap
 * Jagged Worm
 * Killer Mantis
 * Kobold
 * Land Anemone
 * Large Nepent
 * Little Nepent
 * Lizardman Lord (Level 82)
 * Lungfish
 * Pup
 * Ragout Rabbit (Super Rare)
 * Ruin Kobold Sentinel
 * Ruin Kobold Trooper
 * Storm Hornet
 * Treant Sapling
 * Trembling Cow
 * Trembling Ox
 * Wind Wasp
 * Wolf

Known Plants

 * The Flower of Pneuma

Aincrad (ALO Version)
At the end of Fairy Dance, with the sprouting of « World Seed », Kirito brings up Aincrad flying castle, generated from the simplified Seed program. It is essentially identical to the original Aincrad, except for a few key features.

First, the bosses and dungeon monsters were made significantly more difficult, as there is no threat of real death in the ALO Aincrad. Dungeon maps, bosses, and similar features were likely re-done, as the Clearers in ALO continue to utilize mapping and scouting strategies on bosses.

Since Aincrad was fused with ALfheim Online's gameplay, the system was also designed to re-account for magic, flying, and the new limitations and additions with Sword Skills. It is now possible to fly floor to floor in ALO's Aincrad, through there is an invisible wall at the highest front line floor. Dungeons are no-flying zones, and the remain-light system was incorporated from ALO.

It is currently being cleared by guilds and the like, led by high level players like General Eugene.