Hidden Palace Zone did not originate from fanon, and more information can be found on their respective wiki(s). You may read more about it on the following wiki(s):

Hidden Palace Zone
Sonic running through Hidden Palace Zone in Sonic 3 & Knuckles
Greater Location Angel Island
First Appearance Sonic 3 & Knuckles
Location Type Temple
Hidden Palace Zone is a location in the Sonic series. It has made appearances in Sonic & Knuckles and is the ancient Echidna temple.

Fanon Appearances

Sonic Heroes 2

Hidden Palace Zone makes an appearance in Sonic Heroes 2. It has fallen into a state of disrepair due to the Echidnas clearing out into Mystic Ruins North and therefore the only habitant for the past 10+ years has been Knuckles. This changes upon Knuckles and Shade falling in love.