Emphramite,
You know, the book The Hollow Earth, by Raymond Bernard (pen name) does confuse the hollow portion and the worlds within the crust. It speaks of reaching Shamballa in the hollow earth through the crust. You know, you would have to pass through some layers where the physics of those worlds is completely different, and the creatures. You would have to pass through hellish environments.
Anyway, they are two separate places. The hollow earth is on the surface of the earth. There are humans there. In times past, the Eskimos spoke of receiving eskimo populations from the North, so they myust live at or near the neck on the openiing.
The animals walk in and out when they hibernate. When Olaf and his father sailed in and out, they never left the sirface.
Dean