If the ruins were really stone monuments, it would have taken quite an advanced civilisation to crave them. Meaning, they will be as mysterious as the statues on Easter Island.
The stepped stones reminded me of another place in Japan. Along the coast of Miyazaki on Kyushu, there is this rock formation called the Ogre's Washboard. It is formed extrusive igneous rocks cutting the surface at an angle and weathered over the ages. The formation stretch for ten of kilometres along the coast facing the Pacific Ocean formng quite an impressive sight.
Incidentally, in Japanese Shinto mythology, the area around Miyazaki is known as Himuka, meaning Land Facing the Sun. It is told that Jinmu, the first emperor of Japan was born here in Himuka.