By Asit Jolly
BBC correspondent in Chandigarh
A 68-year-old British Sikh has begun a 4,000km (2,500 mile) walk from India's northern city of Amritsar to the country's southernmost tip to raise £1m for cancer and HIV research.
Mr Grewal has already run in London marathons
Inspired by British woman Ffyona Campbell's journey across Africa in 1993, Balwant Grewal, who lives in Buckinghamshire, southern England, decided to hike the length of his native land - India.
Born in India's Punjab state, Mr Grewal migrated to the UK many years ago and established a successful real estate business from his home in Denham.
Now, close to retiring, he is travelling from the Holy City of Amritsar to his destination in Kanniyakumari in Tamil Nadu.
"'Ffyona Campbell traversed the length of Africa, where almost a fifth of the population is threatened by HIV and Aids. I want to focus the world's attention on the Indian subcontinent where the situation is becoming equally alarming," Mr Grewal told the BBC.
Mr Grewal said his motivation to do something meaningful about cancer came after he learned that a Polish immigrant neighbour in Denham was dying of the condition.
"We were not close friends but Peter, who would simply wave a cheerful greeting to me each morning, was dying. That set me thinking," said Mr Grewal.
His endeavour is already beginning to pay off, with several Punjabis coming forward to pledge funds. More than £100,000 has been contributed by Indians living in the UK.
"People in India are reluctant to talk about Aids but I must say they are being most generous. Many have already contributed," Mr Grewal said.
Having run the London marathon many times, Mr Grewal says he is fully confident of completing his long task.