In 1865, with his cousin Mani Singh, Nain Singh left Dehra Dun, the Geometrical Survey of India's northern India headquarters for Nepal. From there Mani returned to India by way of western Tibet, but Nain went on to Tashilhumpo, where he met the Panchen Lama, and Lhasa. During his stay in Lhasa, his true identity was discovered by two Kashmiri merchants, but for unknown reasons, they did not report him to the authorities. Nain Singh returned to India by way of Mansarowar Lake in western Tibet. He had mapped the trade route through Nepal to Tibet, determined for the first time the location and altitude of Lhasa, and mapped a large section of the Tsangpo, the major Tibetan river.
On a second voyage, in 1867, Singh explored western Tibet and visited the legendary Thok-Jalung gold mines. He noticed that the workers only dug for gold near the surface, because they believed digging deeper was a crime against the Earth and would deprive it of fertility.
In 1873-5, he traveled from Leh in Kashmir to Lhasa, by a route more northerly than the one along the Tsangpo that he had taken on his first journey.
See also: Krishna Singh