Virtual Lab

Floating City is located at the top of World Tree. It is a city where King Oberon and Queen Titania live. Players that can reach the top of the World Tree get to meet King Oberon and will be reborn as an Alf and are granted unlimited flying. Reaching the Floating City and meeting the King and Queen is the main quest in ALfheim Online.

However, as Kirito discovers in Episode 24 when he reached the top, the city does not actually exist.

Background
To reach the Floating City, the player must go through a dome at the base of the tree, which is guarded by MC guardians.