In several parts of the Asuka region of Japan there are unusual carved granite stones and the largest of which is known as Masuda no iwafune (The Rock Ship of Masuda). This large granite stone has 2 openings on its top surface. Theories that it is Masuda Pond Monument's pedestal, or it was a tool for astronomical observation, or it was an Imperial Mausoleum's stone cellar exist, but there is no