You also have to consider the author is located in Switzerland, which has a much different construction style when compared to, say, California.

In order to actually lay wiring underneath a masonry wall, you need to rent/own a wall chaser, be aware of where existing cable runs are, and be prepared for a lot of work: prepare the room for dirty work (cover the floor and furniture, isolate the affected rooms from the rest of the house), do the actual cutting work, lay the conduit, re-plaster the entire run, re-paint it (sometimes re-paint the entire wall if you don't have a good color match), clean up. You're basically looking at an entire day of work if you're doing this solo, plus prep. And it's pretty much never doable in any rental.