said by Jon:
They unscrew this then there's a pipe that leads down to the valve. Can't find a picture of that but it's below the frost line.
We do have one of those rusted circular access points in the front yard but it is about 10ft from that basement corner and also buried under lots of snow and ice at this moment. However, they are somehow reading the meter (from the outside) even in winter.
I will open the cover of the enclosure tomorrow and post a photo of what is there - hopefully not a bunch of rats. I regret not being more curious about the plumbing and HVAC stuff all these years.
*** Found official info. Water meter is supposed to be on the front wall of basement which includes that corner enclosure. But the recently installed radio transmitter is obviously outside since nobody came into the house.