Complex sentence: They follow the stream to a high mountain cave called Broke Tooth Mountain, they enter the cave, the ground of the cave is carpeted in crushed bone, and they are attacked in the dark by an unknown creature.
Split into simpler sentences: They follow the stream to a high mountain cave called Broke Tooth Mountain. Upon entering the cave, they discover the ground of the cave is carpeted in crushed bone, before they are attacked in the dark by an unknown creature.