"We (the yatris) were returning from the Chinese side and there was solid fog all around us. The air was so thick that you couldn't see the tip of your fingers," Mr Roy recalled.
The group of pilgrims to Mansarovar was walking towards the Lipulekh Pass when they found themselves lost in the fog.
"We had no idea where we were. But, as we were walking, we heard some people speaking in Hindi. That was when we realised we had reached India," the 72-year-old governor and former BJP leader from West Bengal said.
It was August 15 that day, he said.
"So it was wonderful," Mr Roy told PTI on the sidelines of a book launch here last evening.
The high-altitude Kailash Mansarovar pilgrimage spot is in the Tibet region. There are two routes to this -- through Lipulekh Pass in Uttarakhand and Nathu La in Sikkim.
Ms Chadha had also led the Mansarovar Yatra team that Mr Roy was a part of.
"I think that trip instilled a sense of wanderlust in me and I was bitten by the travel bug. Since then, I have travelled to many places. I have been on the Amaranath Yatra, went to Vaishno Devi and visited the Valley of Flowers in Uttarakhand, among other places," he said, adding that the two destinations that he had not yet visited were Gangotri and Yamnotri.
Mr Chadha said she hoped the book would serve as "a guide and a knowledge storehouse" for the next generation on Dalhousie and its history, and prompt them to travel to the hill town in Himachal Pradesh.
Dalhousie is in the Chamba district and is situated on five hills.