I live in a pretty hot climate, but it’s only really unbearable at times due to shoddy building and bad urban planning. Even then, summer can be difficult.
I can’t imagine what it’s like on the equator, especially in dense urban centres. What’s Mumbai, Bangkok, or Singapore like at the height of the wet season?! How do millions of people function day to day?
Have a look at the map here, and also at the satellite view. Zoom in: 37,0593067, 15,2976834
It is a >2000 year old town, still alive and inhabited (mostly by tourists nowadays). People had no air condition back then.
The buildings are made of natural stone. The walls are as heavy as possible. The streets are as narrow as possible (some can be used with a car, some cannot).
I have been there on vacation for two weeks and the effect of this way of building a city is huge! The sun barely reaches the ground in these narrow streets. The heavy walls do not heat up much in the lower floors. They keep some the ground’s coolness - and today, some of the air condition’s coolness as well, but the local people told me that they use their air condition only in the 3-4 hottest month’s of the year.