Yeah, I lived in Switzerland for a time, and they're pretty normal there too. When it got hot, sometimes I'd throw the windows wide open at night and let the place cool down to 20ish. Then, around 9am I'd shut all the windows and shades. I was also lucky because I had windows on opposite sides of the apartment, so I had good cross ventilation to blow the heat out.

When I'd come home it would be low-20s or mid-20s inside, while outside it was above 30. But, like you said, if the heat wave lasted too long, the concrete would heat up. I'd still throw open the windows at night, but once the concrete of the building was up to about 30 degrees, even if it dropped below 20 at night, it would still be 25ish indoors in the morning.

At that point, when it was 25ish indoors, below 25 outside (but heating up) and 30ish degrees in the walls, I wasn't sure if it was smarter to shut everything and try to keep the warm air out, or open things and hope that the ventilation allowed the concrete to cool.

Also, at night even though cross-ventilation was a good plan, and it cooled things off, I lived in a loud neighbourhood (by Swiss standards) and it was so much easier to sleep with the windows shut. Those windows reduce the noise from outside so much.