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The earth itself is warm there - in these places heating pipes run close to the surface. Usually, a small room is made underground, in which the technical equipment of the valve, sensors, etc. is located. The temperature in it is high, it is very hot there - this is why the earth warms up.) And iron covers are not ventilation, these are access points to such premises.)

I hesitated when I was about to type "vent"..... because I wasn't really sure what they were, but I thought since the cats seemed to be hanging around it, that warm air might be coming out. Thank you for the explanation about the heating pipes.