It sounds far worse than it is. You drop onto the square X: 13 Y: 27. To get out you'll have to find another cave with an opening at X: 32 Y: 16. From there, just walk to the island in the middle of the lake, located at X: 32 Y: 12, press the encounter button and use some sort of water breathing device (NO, that's not oxygen tubes…) and you'll end up in another cave. This other cave is actually the home of the blue dragons mentioned in the chapter before this.
Other places of interest are a house at X: 74 Y: 15 with an inhabitant not able to escape and some snakes at X: 61 Y: 31.
There's a lot of secret tunnels through the mountain down here and we're not able of making a map so you'll have to find your way to the places mentioned above by hitting rocks now and then…
