There was an episode of Loveline (the radio show) ~20-25 years ago where a young woman called in who grew up in a large mansion. Part of what she brought up was that there was a man who lived in the walls/unfinished spaces of the wing of the mansion her bedroom was in, and I believe that one of the exits from inside the walls just happened to be her bedroom closet. Basically every kid's worst nightmare.

Check out this wonderful, unforgettable spanish movie on that theme, much better than any plot summary could suggest (and also I don't want to give spoilers) : The Uninvited Guest (El habitante incierto)

https://www.imdb.com/title/tt0436374/

Taking the theme to a fantastic extreme is the amazing french miniseries Beyond the Walls (Au-delà des murs), which has a whole bizarre world secretly living in your house.

https://www.imdb.com/title/tt4999820/

I was reminded of the college student who found a guy in her closet wearing her clothes:

https://www.google.com/amp/s/www.buzzfeednews.com/amphtml/cl...

Well . . . Enumclaw, after all. That somehow seems tame.

http://tonsoffacts.com/25-fascinating-and-amazing-facts-abou...