Other mistake: There's a scene where they turn a wheel to control the flow of water into a much larger chamber. The cavern that is presumably completely filled with water (water is dripping off the ceiling) is massive. The flow from the smaller chamber into the cavern is relatively small. They enter moments after stopping the flow to find the cavern is drained. It should A) either take the cavern a very long time to drain or B) the cavern should never have been fully filled with water.