Koridai is a densely mountainous island. It features multiple mountain peaks that climb high above the territory and surrounding ocean. The mountainous landscape gives the island a hostile environment, which includes canyons, wastelands, active volcanoes, and waterfalls torrenting down the mountain sides, most prominently in Spearfish Falls. It also has a frozen tundra in the northwest where Nortinka and Serigon Caves are found. During Ganon's siege of Koridai, several of the island's regions were conquered by his henchmen: Goronu (Boss), Harlequin, Militron, Glutko (Boss), and Lupay. These regions were turned into the Face of Evil, mountain peaks and structures with angry glares in the likenesses of Ganon's minions, which now serve as their bases. Koridians were then enslaved in these areas and transformed into monsters. Ganon also has his own Face of Evil, Ganon's Lair, which sits in the center of Koridai.
The island is home to a few small settlements. These include a small fishing village along the coast of Crater Cove and a couple of fortresses, most notably Fortress Centrum. However these became inhabited by Ganon's forces following their take over. Several islanders have managed to evade capture and taken refuge in small houses and caves scattered across the island. The island's only known store, Morshu's shop, is located in the Goronu Stage.
Link travels with Gwonam to Koridai when news breaks of Ganon's take over. Together the pair journey to the Faces of Evil and confront his minions. Eventually Link and Gwonam realize that Ganon kidnapped Princess Zelda and hid her in Koridai under a sleeping spell. After defeating Ganon's minions and reclaiming the Faces of Evil, Link travels to Ganon's Lair and defeats him with the Book of Koridai. He afterwards locates Zelda in the final room and wakes her up. Koridai is then said to return to peace once more.
- "Your Majesty, Ganon and his minions have seized the island of Koridai!" — Gwonam (The Faces of Evil)
- "These are the Faces of Evil. You must conquer each." — Gwonam (The Faces of Evil)
- "Koridai has fallen to Ganon and his evil friends! The gentle islanders are being transformed into blood-thirsty warriors." (The Faces of Evil manual, pg. 2)
- "Rumors are circulating that while you have been traveling to Koridai, Zelda has disappeared from the Palace! Could it be that Ganon has used his magical powers to kidnap her?" (The Faces of Evil manual, pg. 9)
- "Look, already Koridai is returning to harmony! The birds are singing! Isn't it beautiful?" — Gwonam (The Faces of Evil)