Closets work well for getting from one floor to another. Have you considered that? Cables can also be snaked through most walls with some effort. Other possibilities are the pipe runs that your pluming uses to vent drains to the roof. Attics, basements, and crawl spaces work well for horizontal runs. I have two network legs and updated telephone lines that run through my house. They are more than 100 feet long, go through two levels, and from one end of the house to the other. My house is old and it wasn't easy, but it was well worth the effort. My Wife, Son, and I did the work and it took some planning and a couple of hours per run.
Yes, I will always push people to run cables inside, no matter how difficult it is. They are not as dangerous as external wires and last much longer. I have installed hundreds of networks, some of them in buildings over 100 years old. Only one them had an above ground, outside leg. It was hit by lightning. Luckily, it only destroyed two computersóburned them up! No one was using them at the time. Larry