It can get above 30C here[1][2], which is pretty hot for us. As you say, buildings are well insulated for the winter which means that the walls retains a lot of heat into the night once they've been baking for several days.

Keep in mind the sun goes down at around 11pm, so it doesn't really get cold outside until well past midnight. In my home, that means it can be 25C inside for hours after bedtime unless I use AC and keep the interior cold during the day.

One could get used to 25C I suppose, problem is it's just for a few weeks at a time, then it goes back down. So you never really get used to it.

[1]: https://www.yr.no/en/statistics/table/1-72837/Norway/Oslo/Os...

[2]: https://www.yr.no/en/statistics/table/1-72837/Norway/Oslo/Os...