After several years in Utah and Wisconsin, learning to live with long periods of warm temperatures (90-100 F, 30-40 C), I find it interesting to observe how Europeans are dealing with their current heat wave. For them, it is difficult to live with temperatures that people in other places around the world are used to and relatively comfortable with.
It is a reminder of how adaptable humans - and life - is.
We adapt biologically, mentally and with our behavior. In terms of heat, I noticed that during the summers in Utah where worked outside daily in temperatures up to 100F/40C, I adapted physiologically to the point where it seemed relatively comfortable. Being in a cooler space, especially air conditioned buildings, was very uncomfortable. This summer, I have spent much time in an air conditioned space (not my preference), and notice that I have not had an opportunity to adapt to even the low 90F (30-35C) temperatures we typically have here east of the Cascades.
There are also many behavioral tricks to deal with the heat: Getting up at or before sunrise and get most of the activities done by mid-day. Drink lots of water to prevent dehydration. Stay in the shade. Use a hat. Find a breezy spot or use a fan. Cool the house during the night by opening windows and doors, close everything during the day. Use external shading for windows. Build buildings that stay cool without air conditioning: external shade (deciduous trees, louvers), good insulation, designed for airflow (low - incoming cool air - and high - outgoing hot air - openings for cross ventilation), cooling towers, etc. Plant trees in the city to reduce the overall temperature (hard surfaces and lack of vegetation raises the temperature of cities 6-8F).