The boot prints seem to be moving around the hatch and then leading into the forest, where they are lost in the pine needles blanketing the ground. (The snow is mostly in the trees, not on the ground under the trees.) Bolt would guess they are a men's snow boot, sized 12-13. Not a small person, but not a Hulk either.

The hatch has a wheel for opening, but does not seem to have a lock. It appears that it would keep out animals, weather, and maybe even nuclear fallout, but not someone looking for shelter.