The Hidden Palace is a location that appears in Sonic the Comic series published by Fleetway Editions. It is an ancient underground building on the Floating Island, most noticeable for hosting the island's Emerald Chamber.
Countdown to Disaster
In the present day, following a nasty hunch Knuckles took Sonic through the Hidden Palace as the Death Egg II was preparing to take off from the island. There, they found Metallix, who had stolen the Master Emerald for the Death Egg, whom the heroes followed to the Sky Sanctuary Zone.