Fan under the window?

The other day when I was walking down the alley surrounded by the apartment buildings, I noticed for the first time there were some kind of covered holes under the windows. I guess I never noticed them during the winter time, as it gets DARK(!) around 3pm.

Anyway, I asked my hubby, and he said they were fans. It makes sense to have a built-in fan there, as you can bring the outside air into the house without opening up the window at night or on rainy days. Given the fact that some windows didn't have them, I guess they were installed by the onwer of each flat. I also heard that most of the older buildings have thicker walls that it doesn't get too hot inside the house. Maybe fans are more popular and suitable here than air conditioners.