Yiyuan Jiutian Cave (Cave of the Nine Heavens) is set deep into the Paleozoic limestone underneath the south flank of Mount Lu in Shandong province. It is named after the Nine Heavens of Chinese mythology, each of its nine natural caverns representing one layer of heaven. Visitors exploring the cave can let themselves be transported to the mythical heavenly palace. In 2001, a team headed by the president of the Chinese Cave Research Association, professor Zhu Xuewen, mapped out the cave system. They then laid out electrical lighting and prepared the cave to give visitors the best possible caving experience.