@0xabad1dea
Well, here in Austria all newspapers remind people to keep darkening thicker curtains and roller blinds etc. closed during the day and to aerate their rooms only during the colder night hours.
Not that nights are much colder in the city anyways though
What they forget to recommend is to stick mirror foil to the window-glass (helps a lot!) and to cover your windows outside with stuff like thin thermal blankets during very hot days (using velcro tape for removability is ideal).