According to the Junior Woodchucks' Guidebook, Marco Polo saw the Lost crown of Genghis khan during his search for the real land of Prestor John in China.
Marco Polo claimed to have found Prestor John’s Land and told Kublai Khan of it when he reached Cathay. Kubla invaded Tibet and moved into the kingdom. He moved the treasure of the Mongul Empire (the entire treasure of the biggest empire in history, including the Crown) in Tralla La for safekeeping since the place was quite inaccessible.
Khan sealed the entrance of Tralla La himself and beyond the gate he installed a mechanism of destruction, a sluice gate that would stop the flow of the sacred whirlpool and flood Tralla La to the mountain tops.
Kublai is said to have loved nature and science and he and his warlords made Tralla La their secret retreat, making slaves of the Tralla Lalians. One day he left and never returned. He and his generals took the secret of Tralla La to their graves.
Eventually all evidence of Kublai Khan's occupation were gotten rid off. Scrooge McDuck and his nephews accidentally closed the sluice gate, which caused the near destruction of Tralla La, but was eventually fixed by Donald Duck. Donald also destroyed the mechanism that controlled the sluice gate, so that should no longer cause a problem.