Holy Summit, spelled "Holly Summit" in the Japanese release, is both an area and an arena in Sonic Battle.
On the Holy Summit map, one can find both Knuckles the Echidna and Chaos, and can also go to the Death Egg during Emerl's story. Chaos' battle arena has the same name, and is a snowy mountain-like region with a giant hole in the center and several smaller holes in the corners. This is where Chaos can be unlocked when on Emerl's story mode.
Holy Summit has two arenas: Chao Ruins and Holy Summit.
Sonic, Tails and Emerl head to Holy Summit, seeking help with Emerl. Chaos Gamma appears and challenges the trio to a battle. After defeating him, they continue on to Knuckles' house. There, Knuckles mistakes Emerl for Phi and attacks him. When Knuckles realizes that Emerl isn't Phi, he decides to help him, Sonic and Tails.
In Tails' episode, Tails and Emerl travel to Holy Summit to evade the pursuing Guard Robos in Central City. Whilst there, Tails and Emerl meet Knuckles who attacks Emerl when he doesn't obey him. Tails then asks Knuckles to accompany him to Emerald Town, so he tells him and Sonic what he discovered about Emerl. Before they can depart however, the trio are attacked by Chaos Gamma. Knuckles then offers to hold Gamma off whilst Tails and Emerl escape to Emerald Town.
In Shadow's episode, after Emerl has been fully awakened, Shadow asks him to fight everyone before he and Shadow fight again. Knuckles can be found at the Chao Ruins.
Emerl comes to Holy Summit after learning about Eggman's master plan, Whilst there, the large crater at the summit floods and freezes over and Chaos appears. The player can then challenge Chaos to a battle, after which Chaos will be unlocked for the Battle and Challenge modes.