The Hidden Palace is a building on the Floating Island. In ancient times, the royal family ruled the island from here. The most notable room in the palace is the Emerald Chamber, home to the Chaos Emeralds and the island's current controls. Other rooms lead off from this central chamber, including living quarters, the Guardian Emerald and a store for Guardian Robots, amongst other things.
Although the area is technically seen every time the Emerald Chamber is featured, the Zone was only named in one story: