Lighting a room that was built wrong
Most unpleasant interiors are not badly proportioned. They are badly lit, and that is fixable.
The complaint is usually about shape — too narrow, too tall, too boxy. Photograph the same room under three different lighting setups and the shape stops being the problem in two of them.
One overhead source flattens everything and pushes the corners into gloom, which is what makes a room read as a corridor. Two or three low sources at different distances give the eye something to measure depth against.
This is the cheapest intervention in the building. It is also the one people skip, because lighting arrives at the end of a refurbishment when the money has already gone.