The broken boxy thing surrounding the metal pipe looks like a pretty standard chimney liner, maybe a piece that broke off and fell down the floor of the firebox. The metal pipe looks like stovepipe, doesn't it? You say it goes from the roof to the crawl space? How peculiar.

I would look around for a professional opinion. I engaged a chimney sweep once who turned out to be a retired fire chief for one of the towns around here, and he gave me some good advice. Basically, I can't burn stuff in my fireplace without risking a chimney fire. Disappointing, but good to know!

vjrnts is correct. The large box shaped object is almost certainly a terra cotta tile used to line chimneys. The fact that it seems to have dropped out of the chimney suggests that the lining is badly damaged. It might, however, have been placed where it is deliberately.

The galvanized stove pipe was probably used to vent something in the cellar. This would be contrary to codes and a possible danger, especially if it has lots of angles and has not been cleaned. By all means check to see if it's still connected to something such as a water heater or even furnace.

Fireplaces of this size and design were intended for coal rather than wood. I second the idea of an inspection by a certified chimney sweep or perhaps your local fire department.

Thank you for the replies, now that you mention it venting something in the basement, it's almost certainly the water heater.

So I would need to vent that elsewhere to use this fireplace for anything at all. :(

This is disappointing, but at least I know now. Thanks again