There is a hatch apparently leading down under the church next to the graves. The hatch is locked, and the lock cant be picked, but i have so far been unable to find anyone suggesting how to get down there...
If you protected the drunken soldiers against their captain, go talk to them in the barracks and they'll tell you about the captain's vault beneath the chapel. There's also a book in their room in the barracks where the captain writes about it.
Ah. Go figure then. I didn't protect em. I saw them out on the map a bit later, getting killed by a troll... Guess i ain't getting in there then. (Already looted and read all the books i could find, so i assume the book also only spawns if you protect em.)
Nah. He just things "join the guards, see the world they said" or something similar. I've cheated my self out of the loot down there. Luckily, there isn't THAT much down there.