In the last half an hour since your completion of the tower project, we managed to find Bob's location. He was one ugly piece of work! However, we weren't able to arrest him for long, Bob broke free and ran to an unknown location. We're still trying to find him. But he left his zeppelin (also called a zephyr, or an airship) here, and we find that this would be a good opportunity for you to recover some of the crystals he left behind. OK. We'll leave you to it.
