Legend claims that, in the mid-15th century, heaven sent Emperor Le Loi a magical sword, which he used to drive the Chinese from Vietnam. After the war a giant golden turtle grabbed the sword and disappeared into the depths of this lake to restore the sword to its divine owners, inspiring the name Ho Hoan Kiem (Lake of the Restored Sword).
The area is best from Friday to Sunday: nearby traffic is banned between 7pm and midnight and a public-square, funfair vibe takes over.
Every morning at around 6am local residents practise t’ai chi on the shore. Sunset is a lovely time to explore the lake too, and can make for some sublime photographs as the sun sets.
The ramshackle Thap Rua, on an islet near the southern end, is often used as an emblem of Hanoi. A number of elegant pagoda-like stone gateways can be found around the lake, inscribed with chu nho Chinese characters, including Hoa Phong Pagoda (Thap Hoa Phong) near the southeast of the lake shore.
You may often bump into small groups of Hanoi university and high-school students out interviewing foreigners to practise their English. They are invariably polite, often very interesting to talk to and provide an opportunity to interact with local youngsters, while they get the chance to improve their language skills (which the Vietnamese are highly ambitious about)!