Aincrad

Aincrad is a floating castle made of iron and one of the main locations in Sword Art Online. This location served as a home for 10, 000 trapped players for two years. This is where Kirito and Asuna Yuki first met, along with Yui, and Heathcliff. Aincrad continues to float high in the skies throughout the days and glows gold in the night. The Castle is comprised of 100 floors, each gateway guarded by a monsterous creature, defeating each one opens a new passage to a new floor in the castle. When the castle is conquered, it fell apart upon Heathcliff's demise, but returned through the magic of The World Seed.

Trivia

 * Because this world is animated, Aincrad is a part of Toon Town.