The Hidden Palace Zone was a region on Angel Island and home to the Hidden Palace which was possibly thousands of years old. Its existence was unknown to even the Guardian Knuckles. It was discovered by the Dark Legion in 3237 after they discovered the secret portal ring to its enterance. After Locke entrusted the Master Emerald to the protection of the Dark Legion, Lien-Da had the Master Emerald moved from Haven to the Hidden Palace where it could not be located by the forces of the Eggman Empire. The Hidden Palace Zone as a whole acted as the Dark Legion's hidden base of operations to act as Angel Island's resistence movement against the Dingo Regime under Kage Von Stryker's rule, and it was where the few rescued echidnas lived in freedom. After Sonic the Hedgehog and Knuckles arrived on Angel Island along with the Chaotix, they were brought to the Hidden Palace by Dr. Finitevus. Once there, Lien-Da took them through the palace's chambers, where an ancient tapestry was hung up on the wall that was there when the Dark Legion located the Hidden Palace. After briefly discussing the tapestry, the three went in and viewed the Master Emerald in the palace's underground shrine.
Although Sonic, Knuckles, the Chaotix and the Dark Legion managed to successfully liberate Locke from captivity in Cavem Canus, at the same time Dr. Eggman dispatched Hunter to retrieve the Master Emerald. Locating the Hidden Palace, he proceeded to capture numerous echidnas and teleport them to the Egg Grape Chambers. Although he managed to get close to the Master Emerald, its energies reacted within Knuckles and transformed him into Super Knuckles, at which point he smashed through the roof of the Hidden Palace and hurled Hunter off Angel Island to his death. Although Dr. Eggman had learned of the Hidden Palace's location from Hunter, the Master Emerald was moved to a new safe location.
During Geneisis, Knuckles guarded the Master Emerald in the palace again, but this was eventually changed back to normal.
