Hong Kong's Kowloon Walled City once had a density of more than one million people per square kilometre. "Living in Kowloon Walled City was so tough," says former resident Albert Ng. The Walled City started as a Qing military fort in the 19th Century. After the First Opium War, Britain took control of Hong Kong Island, and then expanded its control into parts of mainland China. This led to the leasing of additional territories to the British for 99 years - but Kowloon Walled City officially rema