After taking out the Drow/rogue elves, the party can move on down the tunnel, which continues to slope downward. There is still no natural lighting. After about twenty or thirty minutes the tunnel does get subtly lighter until it's almost like sitting in a room with lamp light. As they round a corner they will see a large cavern below them as they come out of the tunnel and are on a ledge. The ledge continues down into the cavern, running downward to the right of where they come out of the tunnel.
The sight below is interesting. There are dozens of buildings below, a small pond in the middle, the sounds of many echoing up from below. There many tunnels out of the cavern, with terraced mushroom farms on the sides of the cavern. There doesn't seem to be any patrols, but all the people that are seen below appeared to be obviously armed. There is a mix of races below, with none really dominate, of humans, elves and dwarves. Lighting seems to be produced my crystals in the ceiling of the very tall cavern. The party can assume they are magical.
Tomorrow: A rough map of the cavern.