Muspelheim

Muspelheim (ムスペルヘーム, Musuperuhēmu) is one of the hardest field dungeons during the Ragnarok Quest, created along with Niflheim by the Cardinal System. It is heavily infested with Eldjötnar, humanoid-type evil-god class boss monsters, similar to Jotunheimr before the completion of the Holy Sword of the Ice Palace Quest. It is also the home to Surtr and Sinmara.

Description
Muspelheim is the realm of fire, clashing with Niflheim, the realm of ice. It has three underground floors. The base floor is filled with Eldjötnars, powerful giants gifted with the power over fire. To advance to the next floor, faeries daring to venture the dungeon must fight the Eldjötnars along the way. The second floor is guarded by Sinmara, sub-boss for the Revenge of the Bifrost Quest. Upon defeating Sinmara, the players can advance to the final floor, where Surtr awaits.

Sword Art Online: Project Ragnarok
Muspelheim was made available, though not completely, to the players sometime after the completion of the Holy Sword of the Ice Palace Quest. It attracted the attention of many high level players of ALfheim, prompting exploration. However, no one lasted very long to at least find the location of the stairs to the next floor. This is because of the map being incomplete during this time, and the base floor of Muspelheim had only been opened for the sake of raids and drops.

By the time the Ragnarok Quest had officially begun, the map was completed, and many parties of players were able to face Sinmara, but most were unsuccessful in defeating her, much less meet Surtr, the final boss. This was until Kirito's party, allied with the Knights of Round and various organizations in Alfheim, was victorious over Sinmara, and Gwenhwyfar's party defeating Surtr.

After the defeat of Surtr, Muspelheim was then deleted by the system, indicating that it had been successfully cleared.

Known Monsters

 * Eldjötnar - humanoid-type, evil-god class boss monster populating the base floor
 * Sinmara - consort of Surtr, and sub-boss for the Revenge of the Bifrost Quest
 * Surtr - final boss for Muspelheim and king of the Eldjötnar

Trivia

 * Muspelheim is heavily on one of the Nine Worlds in the Norse mythology, bearing the same name and characteristics