There is a door in a building that you can see through it if you are standing on the inside of the door in the building and see out as you normally should be able to as its supposed to have a window in the door. However from the outside looking in its pitch black. It seems like a very exploitable building/door. This building is located in charnarus, directly across from the big hospital in berezino. Screen shots located below at imgur, these screenshots were taken from the roof of the hospital looking at the door.
https://imgur.com/a/crfMW9T