A historical spot in Ba Dinh district, Huu Tiep lake or the B52 lake houses the remnants of a plane shot down by the Vietnamese army during the American war. Read more about the Christmas bombings in any decent book about Hanoi or learn about them from a different angle in Hanoi's museums. A sobering reminder of the war, the area is nonetheless a lively street market at times, school yard at others and generally a great place to explore. Walk north for some quaint murals, and walk south then west to lose yourself in Ba Dinh's maze and watch Hanoians get on with their lives.
The cache is not on private property, not in a banyan tree and will require some discretion.