Deep Valley is a landscape masterpiece created by Guo Xi, a Northern Song Dynasty (960-1127) artist. It depicts the mountainous landscape of northwestern China in ancient times. What ideas and designs did Guo put into this picture? How come the way he perceived the mountains and rivers coincides with Leonardo da Vinci's perception of the natural world? Ling Lizhong, the head of Department of Paintings and Calligraphy at the Shanghai Museum, has a fascinating interpretation of this very vital work.