Buildings in northern Europe are just not built for ventilation, AC and dealing with heat. It’s not a matter of looking, that’s just not how people build here (just like people in Israel don’t build building that handle cold weather well).
Luckily, because of the cold, buildings are well insulated so at least they can seek some cover inside. Granted, it won't reach 40C anyways, but at least houses are built properly over there so it helps a little.
Back in July 2018 we had a month of hot weather in Stockholm (you probably experience it, saw in another comment you moved Sweden -> Spain), temperatures reaching 30C for multiple days and "tropical nights" (air temperature >= 20C during the night), even as a native Brazilian I could not bear how hot my house got, it wouldn't cool down during the night and the next day it'd heat up again. It got to a point where I couldn't sleep and there was a shortage of fans for sale, super basic fans were going for 100€ in the 2nd hand market.
Buildings would not cool down anyway during night in Stockholm due to the very short nights and Stockholm bring by a lake, we do not have cool nights. The only solution is insulation plus AC.
Goes both ways, doesn't it?
Lots of houses in Sweden have basement/cellar floors as well, and if you have good insulation, you manage to keep more of that below-ground coldness around, compared to if air blew freely through the house. At least that was my experience.
> you probably experience it
Fortunately not, moved away from my home country in 2012 already :)
During some 30/35+ waves of the last few summers we kept it below 23 degrees Celsius inside, even over many days of heat.
Until recently I lived in Ireland and people looked at me like I had 3 heads when I talked about air tightness, deciduous trees in front of south facing windows, and eaves/awnings - the idea that you might not _want_ as much light as possible baffled the dinosaurs in planning.
I hope the Netherlands is better but I still see an awful lot of windows with no protection from sunlight. Eaves are perfect (and deciduous trees) because you can angle them such that you get light in the winter but shade in the mid-day summer sun.
It’s subtle differences and when its super hot (40c) you need AC anyway, but upper 20s/low 30s still feel ok in a well ventilated apartment and not so much with one built for keeping the cold out (like in Germany).
It’s also much more common to have functional window shades (like these http://alumgo.weebly.com/uploads/1/4/6/7/14671210/7800745_or...) in Israel than in Germany. In homes I’ve mostly only seen the cheap kind of shades or curtains in Germany, and these aren’t very good.
All the same, with interesting times ahead it'll be a case of choosing to suffer through, changing locations, or rebuilding | renovating to adapt.
All the more interesting as the northern European climate for the next decade isn't exactly locked in and known for certain yet.