How would you explain this sentence in the context? The light through the trees was shadowy at midday, but the water was clear. Belly-dragged up on a flat stone, sitting at the edge looking back in, it was plain to see the bottom of the cave dropped down to make a sort of room down there, huge and deep. Stones were piled like a sand castle underwater, with bits of shining things mixed into the pile. Maybe yellow leaves, or gold coins. It was like coming up inside a storybook. An ancient temple in the forest, and a pirate’s treasure below. The treasure was mostly shells and broken pottery covered with sea moss, mostly too deep to dive down and reach. How would you explain this sentence: the bottom of the cave dropped down to make a sort of room down there? Thanks!