In the city of Whiterun, set into the wall by the entry to the Hall of the Dead, there is a door that shouldn't exist.  Behind the door lies a photo studio which is rumored to have dimensions far greater than would be possible without the use of powerful magics.

 

This, much as Apocrypha was to Miraak, is the Dragonborn's personal realm.

 

You can find it here:

 

https://www.nexusmods.com/skyrimspecialedition/mods/84524