German engineering, Baby!

Most likely for bringing in coal.

As an old spelunker and lover of modern ruins I have to say I envy your experiences in all these old places.

The only holes I see in the walls are where the electrical conduits were removed and the frame for the door ripped out. However, Suaspontas' explanation is much more exciting! heh. ; )

They're not nails! If you look closely at the heads, you'll see that they're hollow. They are just large gauge needles.

Cool shot! Looks like Fallout3 to me. And I believe those are pigeons. not geese.