I saw this while walking yesterday.
It is between 18" and 24" in diameter.
This is what the camera sees when pointed down the hole at 4X zoom. I did not have a measuring tape to run down it to give you a depth.
I passed word along to somebody-who-knows-somebody that they might want to cap this hole. It is in a back-corner of a property that is adjacent to a public walking trail.
I wonder if it is full of hibernating bats. That might complicate things. I suppose topping it with an 8' length of concrete culvert would deter humans but not exclude bats nor provide prime foraging stations for raccoons.