Things me or my parents would do those 40⁰C+ days: Pull down the blinds to block the sun during the day. If the air is considerably hotter outside, don’t open the windows/doors. Wait until there is no difference in temp to do so. If access to water isn’t an issue, once the sun goes down you can hose the exterior of the house, walls and any surrounding concrete/stone surfaces. It will cool it down considerably. If it is really hot I would sometimes put a wet towel on wherever I was feeling the heat the most (usually heads and shoulders/arms). You will need to soak it every hour or so, because it will start to dry and warm up as you wear it. You can sleep like this, too, but you may wake up from the heat under a hot towel that’s nearly dry.