interior windows as kitchen pass through
nice between living room and kitchen
large walk through with glass doors
The pass through is very nice, and not your typical opening.
sound will pass through the door. Of course, this will mostly depend on what the door is actually made of. Generally, 25 is on the lower end of the STC scale (most normal speech can be heard through these doors), 40 is in the middle and anything over 60 should be almost entirely soundproof.
outfitting a pass-through with windows that you can open and close as your needs demand.