How to make something visible only through a doorway?

Hi, I have this room in my scene outlined in red (which is made of separate meshes, not part of the same mesh as the rest of the walls and floor) which is adjacent to the main play area, and since it’s not a player accessible area, I want it to be visible only through this doorway, but not visible from any other angles. any ideas how I can make this?

this room only exists so when the player opens a door (which will be placed later where the doorway is), there’s something on the other side, and not just a black background. but it shouldn’t be visible from the outside.

Do you mean that the player shouldn’t be able to walk into the room? If so, you could add something in the doorway that the character collides with. (There’s multiple ways to achieve this).

I wasn’t quite sure what you meant in terms of it being invisible.

I mean it should look like this: (photoshopped)

so when you look through the doorway there’s a room on the other side (it’s already inaccessible, that’s not an issue) but you shouldn’t be able to see the room from outside the boundaries of this doorway

ended up creating an occluding mesh and applying a 100% black material to it.