From the introduction:
The ninth level of Dragon’s Delve presents a mixture of man-made (or rather, dwarfmade) chambers and natural caverns. It connects to the Pit in the Woods, located just under two miles south and west of Dragon’s Delve. This pit appears to be an overgrown well. It is, however, an entrance into the dungeon where the people of the surrounding area used to dump criminals and lunatics. The populace didn’t know where the pit led, exactly, but they knew that no one dumped into it ever returned. Perhaps it was simply a deep enough hole that those dumped into it died from the fall. The truth is that some of those put in the pit survived in the dungeon. The descendants of these convicts, cutthroats, and madmen have degenerated into a breed of half-men, as much blind beasts as human beings. They occupy the northwest portion of the level.