In 2000, a large-scale excavation was subsequently performed and a sump water system made by gravel stones and the pieces of coin-shape and turtle-shape stonework were found one after the other.
その後平成12年（2000年）に大規模な発掘が行われ、砂岩でできた湧水設備とそれに続く形で小判形石造物と亀形石造物が発見された。