Changeling Mirror Vault
The Changeling Mirror Vault is within the eastern Hylund Forest, not too far from Hylund Lake. The entrance is a 20 foot hole in the ground going down to a rocky looking tunnel leading underground. Entry into the hole revealed for The Party to lead to a cavern system with mimics pretending to be doors, door frames, treasure chests and more. Mirrors oddly lined some of the wall areas with images on them being of The Party but sometimes showing them slightly warped or other scenes entirely. Exploration was cut short when it was realized that the entire cavern structure is actually a super huge mimic. Note that mimics are technically a kind of changeling. So once they realized they were exploring what seemed like the digestive system of a super sized mimic, they tried to backtrack, only to have the mimic close down some passages and trap them inside.
Through some perception and investigation, and frankly mirror smashing, it was determined that since the mirrors are part of the overall mimic, that it had just been messing with their heads. Hidden in a wooden box behind some mirrors there was a stack of research notes from some experiment that had been conducted there. The notes didn't give details other than pointing out that there was a “test subject” of an experiment named Lester and otherwise it noted “orcs”. No further details were given in the notes about the how and whats, and The Party then managed to get the mimic to literally cough them out of the caverns and back to the surface rather than exploring further.