Book Series About a Middle Age Boy Who Discovers A Spaceship

[Psych]

I remember the story being about a boy from a middle age (medieval) type of community. I don't remember much of the plot in between, but I remember he eventually ends up with companions, and at some point finds a spaceship buried underground, which people used to think was a mountain, but was really the ship. Then he finds out that they are descended from people that came from earth, and arrived on their planet to colonize, or something along those lines. I don't know much else, as it was a long time ago that I read the book.