Tucked away on a small jade-green islet in the heart of Hanoi’s Hoàn Kiếm Lake, Ngọc Sơn Temple (“Temple of the Jade Mountain”) is a portal into Vietnam’s tangled history of war, mysticism, and legend. Ngọc Sơn Temple rose in 1841 to honour the national hero General Trần Hưng Đạo, who crushed Mongol invaders in the 13th century, and its story is woven tightly with both fact and fascinating folklore.