Devil's Tower

Devil's Tower is Ganzack's tower which was created in Medaka's home town. It was later reveaed to be a hidden cannon designed to destroy the rest of the island.

History
Herring and all the other male villagers were forced to work on constructing the Devil's Tower, without knowing what it was being made for. Later, during Luffy's battle with Ganzack it was revealed that Devil's Tower was nothing else than a cannon made with the purpose of destroying the whole island except for Ganzack's pirate ship.