If anyplace could b considered the true hear of Hanoi it is Hoan Kiem Lake. The lake is surrounded by greenery and bounded by the Old Quarter and French Quarter. At night and on weekends the area around it becomes a pedestrian walkway where locals and tourists gather for music, dancing, kids activities and much more. It's friendly and family oriented. Always be aware of possible pickpockets, but that's probably the worst of it. Take the time to walk over and stroll the lake. It's nice break from the chaos of Hanoi traffic.