1. an open window to the outside would act like a full range "bass trap."
2. an open door to another room would cause the room to couple with that room...and reduce bass build up...at the cost of symmetry.
3. The problem we have with our domestic listening rooms is that the lower bass waves are much longer than our room dimensions...so the waves build up and give us high decay bass that rings...ironically some people love bass that rings...it's kind of visceral...think audio show bass.
4. As far as sound waves bouncing all over the room? Of course that's what happens in every room.
5. Sound waves are pressure waves. If you blow a hole in a room or find a bigger room...the pressure will be reduced. A window or door is a more subtle example of that.
6. Where does sound go? Sound energy gets absorbed by materials in your room/house...it gets turned into heat. Very low frequencies can of course go through the neighborhood.