Interactive Peephole

I was wondering how this could be done? I have a horror game that I’m working on and I would like to include this. I just need a peephole that you can look through and see a ghost on the other side.

You would probably need a matene that would be forced to shrink and transition to the level of a keyhole, or hole in a wall in order to see through it. Also would have to be unobstructed in order for the hole to be seen through. And you may need to have a trigger for the event to occur.