4th Floor (Aincrad)

The 4th Floor (第4層) of Aincrad used to be a desert canyon-themed floor in the beta version of Sword Art Online, but was turned into a waterway-themed floor in the official service version.

Geography
In the beta test of Sword Art Online, the entire 4th Floor was a gravelly, reddish-brown land that consisted of a crisscrossing web of narrow, intersecting canyons that were sandy at the bottom and impossible to scale. The players had no choice but to travel through the canyons, but the sand made it significantly hard to traverse, while the complexity of the intersecting canyons made it easy to lose one’s way.

Although the terrain was mostly the same in the official version of Sword Art Online, the once sandy cliffs were filled with water and the reddish-brown land was covered in lush greenery.

3rd-4th Floor Stairs
The stairs between the 3rd and 4th Floors were located on a hill, thirty metres across, that was surrounded by cliffs looming over the nearby area, except for two paths to the southeast and southwest respectively, leading to separate canyons. In the official version, the hill was surrounded by water from all sides, thus becoming an island. A single tree that grew uninflated swimming rings, which the players could use to navigate the floor, was located at the north end of the island, beyond the pavilion that housed the staircase.

Rovia
Rovia is the main town on the 4th Floor, located on the north side of the floor, to the southeast from the stairs that led to the 3rd Floor. Although the city had a rather plain and boring design in the beta test of Sword Art Online, it became a bright white town in the middle of a square lake. As stone-paved roads were replaced with waterways, gondolas were needed to different areas of the town.

Bear Forest
The Bear Forest is a large forest located to the southeast of Rovia. Formerly a dry and desolate forest in the beta test, the Bear Forest in the official service of Sword Art Online was brimming with life. Like the forest of the third floor, the branches and leaves practically obliterated the view of the sky, but unlike the equivalent on the third floor, the ground of the Bear Forest is covered with thick, wet moss and little springs.

Fallen Elf Hideout
The fallen elf hideout on the floor is located in a submerged dungeon in the eastern mountains to the south of Rovia. , hidden behind a waterfall. The hideout is part of the Shipwright of Yore and Elf War questlines.

Caldera Lake
The Caldera Lake, a lake measuring about three hundred metres in diameter, is located just north of the center of the floor and is surrounded by sheer cliffs, forcing players to cross the lake to reach the south side of the floor. In the beta test, the lake used to be the mouth of a volcano with red glowing magma bubbling up from the cracks in the earth. In the official version, the volcano was filled with water. The lake is inhabited by the Field Boss, Biceps Archelon, that impedes travel to the southern areas of the floor until defeated.

Usco Village
Usco Village is located to the south-west of the Caldera Lake and is the first village that the players can encounter after defeating the Field Boss. The village consists of several shacks, walkways and open spaces buoyed by balsa-like logs, floating and creaking in the midsts of a crescent-shaped lake.

Forest Elf Castle
The Forest Elf Castle was the base of the forest elves on the 4th Floor, located in the southwestern region of the floor. Unlike the dark elven castle, the forest elven castle is located on land.

Yofel Castle
Yofel Castle was an instanced base of the dark elves on the 4th Floor, located in the middle of a great circular lake several times larger than the caldera lake where the floor’s Field Boss Biceps Archelon resided.

History
In Sword Art Online, the 4th Floor was unlocked on December 21, 2022, after the defeat of the third Floor Boss, Nerius the Evil Treant. Asuna and Kirito, the first players to set foot on the floor arrived at 13:12 Aincrad Standard Time. As the only way to navigate the floor was through the water, the two spent some time considering how to proceed, before Kirito realised that the tree growing on the island was the key. After leaving a parchment with instructions to the other members of the raid, the two used swimming rings obtained from the tree to reach Rovia, where they activated the Teleport Gate an hour after the defeat of the third Floor Boss.

With Argo’s help, Asuna and Kirito discovered a quest to craft a gondola and thus travelled to the Bear Forest to gather materials for it. Due to Asuna’s insistence, they searched for the bear king to acquire the best materials for their gondola. However, when their search finally succeeded, they discovered that the bear was not only huge, but also had a fire breath attack. Despite this, the duo decided to try fighting the bear and managed to defeat it after a fifty-minute-long battle.

Having returned to Rovia, the two immediately visited the shipwright to deliver the materials to construct their gondola. Three hours after the shipwright descended to his workshop, the gondola was completed and its new owners left the workshop with it, only to encounter sudden hostility from other gondoliers. Noticing that their quest was still in progress, Asuna and Kirito returned to the shipwright, who instructed them to follow a specific boat leaving town.

At 16:30 that day, Asuna and Kirito spotted the boat and followed it to a submerged dungeon outside of the city. After six hours of navigating the dungeon, the two found the sailors dealing with a group of fallen elves. Once the sailors left the area, the two infiltrated the hideout to investigate the contents of the boxes the sailors had given the elves. To their surprise, the boxes were actually empty. At that moment, they heard several elves entering the warehouse and thus hid in the boxes to avoid being spotted. While hiding, they overheard a conversation among several fallen elves about a plan to be executed five days later. Once the elves had left the room, the duo silently returned to their gondola and returned to town.

On December 24, 2022, at 15:00, the Clearers gathered at the Caldera Lake for the Field Boss fight. The boss was defeated in approximately twenty minutes, with Kirito claiming the Last Attack bonus. Once the Field Boss was defeated, Asuna and Kirito began traveling to Usco Village, the closest village south of the lake. Along the way, they encountered Argo and invited her to join them to celebrate their victory. During their conversation, Kirito remembered that it was Christmas Eve and decided to show Asuna Yofel Castle as a gift.

At the castle, Asuna and Kirito reunited with Kizmel and, while talking with her, Kirito realised that the fallen elves they encountered during the Shipwright of Yore quest were actually building ships for the forest elves to invade the dark elven castle and would invade on December 27. Once the ruler of the castle, Visount Leyshren Zed Yofilis was informed of this, Asuna and Kirito were requested to aid Kizmel in retrieving the Lapis Key on the floor. The trio spent the following two days completing the Lapis Key questline.

On December 27, 2022, the forest elves finally invaded Yofel Castle. Despite the effort of the dark elven forces, as well as Asuna, Kirito, and Kizmel, two forest elven ships, including the flagship, were able to reach the castle. Thus, during the ensuing fight, Kirito rushed to Yofilis and convinced him to take part in the battle. With Yofilis joining the fight, the morale of the dark elves skyrocketed and they managed to defeat the forest elves.

In the aftermath of the battle, Asuna and Kirito learnt that the Clearers had already found the Boss Room and were already marching through the Labyrinth towards it. However, Yofilis informed them that the current Floor Boss had a special ability to flood the room. Fearing that the Clearers were in danger, the two decided to rush to the Labyrinth, but to their surprise, Kizmel and Yofilis volunteered to join them in the battle.

With the presence of Yofilis in the battle, the raid was able to reorganise their attack and the fourth Floor Boss, Wythege the Hippocampus, was defeated at 14:32 Aincrad Standard Time on December 27, 2022 by the seven-party plus one extra party raid, with Kirito receiving the Last Attack bonus. Although Wythege’s Water Inflow ability deluged the entire chamber with water, it could be counteracted by Argo opening the door from the outside.

Known Bosses

 * «Biceps Archelon» (Field Boss)
 * «Wythege the Hippocampus» (Floor Boss)

Known Monsters

 * «Dark Elven Gatekeeper»
 * «Fallen Elven Foreman»
 * «Fallen Elven Guard»
 * «Forest Elven Heavy Warrior»
 * «Forest Elven Inferior Knight»
 * «Forest Elven Light Warrior»
 * «Forest Elven Rower»
 * «Forest Elven Spearman»
 * «Forest Elven Swordsman»
 * «Gaudy Nepenthes»
 * «Magnatherium»
 * «Scuttle Crab»

Known Quests

 * «Laketop Fortress»
 * The Fourth Floor quests of the «Elf War» campaign
 * «Shipwright of Yore»