The Lama is searching for the River or Well believed to have been created when Siddhārtha Gautama, the founder of Buddhism, loosed an arrow into the ground during a competition to win a bride.
From The Life of Buddha by A. Ferdinand Herold, tr. by Paul C Blum :
Then they brought out the bows, and skillful archers placed their arrows in targets that were barely visible. But when it came the prince's [Siddhārtha Gautama's] turn to shoot, so great was his natural strength that he broke each bow as he drew it. Finally, the king sent guards to fetch a very ancient, very precious bow that was kept in the temple. No one within the memory of man had ever been able to draw or lift it.
Siddhartha took the bow in his left hand, and with one finger of his right hand he drew it to him. Then he took as target a tree so distant that he alone could see it. The arrow pierced the tree, and, burying itself in the ground, disappeared. And there, where the arrow had entered the ground, a well formed, which was called the Well of the Arrow.