It would be very easy to keep all of that cool as well, with some ice rink technology under it all, and clever control of how air moves. It might be too cold for flies and pigeons!
Oh they do just that. The marble is a special, heat resistant marble with cooled pipes running underneath. It is necessary to keep the place cool in the 120 degree heat. (50+ for you Celsius people)
Heat control, sanitation, and crowd management are huge parts of the hajj process. There are mist sprayers all over the place that spray cool water vapor (kinda like the lines at Disney world), and the air-conditioning system in the Prophet’s mosque is among the largest in the world. The place is regularly sanitized as well. (This was something that was highlighted during the swine flu scare a few years back.
It is no secret that the Saudis have spent billions upon billions of dollars in making the sites the marvels they are today. It is because of science, however, not miracles that they were able to do this.
One only has to view accounts from earlier years when pilgrims died of disease, banditry, exhaustion, and heat stroke to realize that the place is nothing special in and of itself.