Answer: in the wall separating the air conditioning from the outdoor unit for monosplit type models, in ducts located in a false ceiling or in the attic for multisplit type models.
If your air conditioning is monosplit, that is to say that it contains only two elements (1 exterior, 1 interior), the simplest would probably be to install them each on the same wall, on each side. Thus, you will only have to pierce the wall to pass the pipe between the two, it will be more practical or aesthetic from all points of view. For multi-split type air conditioning with many ducts, the most commonly used method is to pass the ducts in a false ceiling or in the attic. They are completely hidden and remain easy to access. The other solution would be to pass them in each room along the walls, covered with chests. The visual rendering will already be much less interesting, it's a matter of taste. You too, send us your brico question