There’s tips that work and some that don’t, but when it gets super hot there’s not really much you can do without AC.
I do the standard things you should do: doors and windows closed during the day, curtains closed all day on the sunny sides of the house. Then you’re only supposed to open the windows once the outside temperature is cooler than inside. On a typical hot day this is, I find, usually around 9pm.
The problem last night was that I went to bed at 11pm and it was 30 degrees in the bedroom. From what I can gather it only came down to below 30 degrees outside from about 10pm onwards. And if there’s no breeze kicking about at that hour, opening the windows doesn’t make much difference.
Ah well. One more night of it, Friday looks a bit more reasonable then back to mid 20s and below which is much more manageable.