From publisher blurb:
Eons ago, they built a temple in the woods to worship the Thing. Who were they? Where did their civilization go? Were they the ancestors of the people who live here now, or were they destroyed by invaders? Whoever they were, they brought sacrifices here and fed them to whatever it was they worshipped. It gave them gifts in return, for they were not a pious, reverent people. They did not send their own beloved children to be devoured — no, they fed their foes to this Thing, whatever it was.
What they got in return was ghost iron, a metal infused with the souls of those consumed. There are alchemists who believe it is made by the distillation and arcane multiplication of iron in the blood, but they have never witnessed the process for themselves. This ghost iron is made on some other plane of existence entirely — presumably where the Thing that makes it comes from — where no human has been. There are others, especially those who have experience with implements made from ghost iron (or what they suspect is ghost iron) who believe it could be made by anyone who can stuff a ghost into a piece of metal.
It is not entirely a fruitless question, either, because this temple is still a source of ghost iron. There are still people who worship there, who can still find the Thing in the Woods at its temple, who still bring sacrifices to it. Perhaps as long as humans have a need for gods to look up to and the gifts they can provide, this temple will never be abandoned.