Okubo Mabu Mining(大久保間歩) is the largest ruins of Iwami Silver Mining that you can enter. It is about 900m long in total and about 150m is open to the public. It's been mined mainly from the end of the Edo period to the Meiji Period. You can see the traces of both modern digging tours and old fashion styles. In the Edo period, governor Okubo entered with his spear and rode on the horse. It was named after him. At the end of the cave, you can see the huge hole created by men's hands.