He set off in January 1866 with his translator H. G. Kennedy, a British Consular official in Bangkok, who saved Thomson's life when he contracted jungle fever en route. The pair spent two weeks at Angkor, where Thomson extensively documented the vast site, producing some of the earliest photographs of what is today a UNESCO World Heritage Site. Thomson then moved on to Phnom Penh and took photographs of the King of Cambodia and other members of the Cambodian Royal Family, before travelling on to Saigon. From there he stayed in Bangkok briefly, before returning to Britain in May or June in 1866. While back home, Thomson lectured extensively to the British Association and published his photographs of Siam and Cambodia. He became a member of the Royal Ethnological Society of London and was elected a Fellow of the Royal Geographical Society in 1866, and published his first book, "The Antiquities of Cambodia", in early 1867. After a year in Britain, Thomson again felt the desire to return to the Far East. He returned to Singapore in July 1867, before moving to Saigon for three months and finally settling in Hong Kong in 1868. He established a studio in the Commercial Bank building, and spent the next four years photographing the people of China and recording the diversity of Chinese culture. Thomson traveled extensively throughout China, from the southern trading ports of Hong Kong and Canton to the cities of Peking and Shanghai, to the Great Wall in the north, and deep into central China. From 1870 to 1871 he visited the Fukien region, travelling up the Min River by boat with the American Protestant missionary Reverend Justus Doolittle, and then visited Amoy and Swatow. He went on to visit the island of Formosa (modern-day Taiwan) with the missionary Dr. James Laidlaw Maxwell, landing first in Takao in early April 1871. The pair visited the capital, Taiwanfu (now Tainan), before travelling on to the aboriginal villages on the west plains of the island. After leaving Formosa, Thomson spent the next three months travelling 3,000 miles up the Yangtze River, reaching Hupeh and Szechuan. Thomson's travels in China were often perilous, as he visited remote, almost unpopulated regions far inland. Most of the people he encountered had never seen a Westerner or camera before. His expeditions were also especially challenging because he had to transport his bulky wooden camera, many large, fragile glass plates, and potentially explosive chemicals.