The Hyakumangan no Iwa Rock is a huge sandstone boulder belonging to the Tetori Group - a unit of rock from a shallow marine environment in the Jurassic to Cretaceous period (201 to 66 million years ago). It is believed to have been washed down from the Miyatani River during a big flood in 1934.
This is a prefecturally-designated national monument and selected as one of the 100 best geological examples. It is about 16 meters high and 52 meters around and weighs approximately 4,800 tons. Why don’t you try picking it up?