It was stuffy in the bedroom because I also run my server in here with UPS battery backup. I have a vent exhausting hot air from my ceiling and needed a way to get cool air from outside.
My door was once made of glass panels, but most of them have broken and the outside of the door was boarded up. I added cardboard into this hollow area as insulation.
I made a wood panel to cover this area. I routered the edges around, added a recessed door (to prevent draft and light) then stained the wood.
Now I cut the hole in my door, matching the door i made in the other piece.
Oh what a mess. Now to glue some window screen fabric to the door and screw on a vent cover on top of that.
Here is a view through my little vent.
With the door closed. No light comes in because I made the pieces fit in perfectly then added weather stripping.
The dog likes the view and fresh air too!