The Underworld is the dwelling place of Hades. Although it is a part of the Olympus Coliseum, it stands apart from the Coliseum in that it is the entire setting for Hercules's story in Kingdom Hearts II. The Underworld consists of two parts, the Cave of the Dead and the Underworld Caverns. The Underworld is also home to the Underdrome where Sora can take part in tournaments. Many bosses are fought in the Underworld, including Demyx, Pete, Cerberus, and Hades himself.
The Underworld theme music is "The Underworld", and its battle theme is "What Lies Beneath."
Kingdom Hearts II
Sora, Donald, and Goofy emerge in the Underworld when they first arrive, meeting Megara, who is on a quest to convince Hades to stop bothering Hercules. When Sora confronts Hades, he summons Auron, who quickly switches to Sora's side. Hades cannot be hurt in the Underworld, so the team attempts to escape, and Auron and Sora are forced to take on Cerberus before they can leave the Underworld. Back up top, Hercules offers the junior heroes the Olympus Stone, which stops the Underworld from draining all their strength, however, the stone has been stolen by someone in a black cloak. Looking for the stone, they encounter and have their first confrontation with Demyx. The team then rescues Meg with the help of Hercules and Pegasus before opening another gateway with the Olympus Stone.
When the team enters the world for a second time, the Underdrome has been unlocked, presumably when Sora used his keyblade to open a wall during the first visit. Hades kidnaps Meg as incentive to force Hercules into the games. The group enters the Pain and Panic Cup, and the final competitor is Auron, who is being controlled by Hades. Hercules faces Auron alone while Sora, Donald, and Goofy retrieve the statue Hades is using to control Auron. By returning the statue, Auron regains his free will and refuses to fight. Hades, as Hercules's punishment, drops Meg into the River Styx, and Hercules jumps in after her. Hades believes he is dead, but Hercules returns for the final battle with Hades, a true hero at last. They defeat Hades, everyone is reuinited, Auron is freed, and Sora, Donald, and Goofy are immortalized as constellations, much to Phil's disbelief.
Tournament Cups
Just like in the original game, this world is home to a series of tournaments that unlock throughout the game. There are four primary cups, and then four paradox cups, which are more difficult than the first four. The first three paradox cups feature the same lineups as their originals, but the final cup is the most intense of any competition. Each cup has its own set of rules and limitations. The following is a list of cups and how to unlock them.
- Pain and Panic Cup - Clear Disney Castle for the first time.
- Cerberus Cup - Clear Agrabah, Halloween Town, and Pride Lands for the first time.
- Hades Cup 2
- Titan Cup - Clear Olympus Coliseum for the second time.
- Goddess of Fate Cup - Clear previous cups and beat Xemnas for the first time.
- Pain and Panic Paradox Cup - Clear all previous cups.
- Cerberus Paradox Cup - All Drive Forms (except Final) at level 5, unlock Paradox : Pain and Panic
- Titan Paradox Cup - Summon level 5, unlock Paradox : Pain and Panic
- Hades Paradox Cup - Clear Space Paranoids for the second time, clear all previous cups, all Drives and Summon at level 7, Standard level at 99.
