This is the entrance to the suspected tunnel in the pasture. We don't know for sure that it is a tunnel, it could be a burrow. We can't see a wall inside to one direction and there is another entrance many feet away in that direction in the pasture, so we suspect that they are linked.
That is my shoe in the picture, to show scale. It's a size 8 woman's shoe. It isn't as far from the entrance as it looks in this picture, it's how the ground is rounded. The entrance really is almost as big as my shoe!
All it needs is a little "Home Sweet Home" sign over it, eh?