David Cameron has visited the Golden Temple in Amritsar, the holiest site in the Sikh faith.
The prime minister wore a blue head covering, an orange scarf and he went barefoot to bake chapattis and prey in the shrine.
It marked the first time a serving British prime minister has visited the Sikh holy city in the northwestern state of Punjab.
He said: "Today was fascinating and illuminating - to go to the place that is so central to the Sikh religion. It is very moving, very serene, very spiritual.
"It was a huge honour and a great thing to be able to do. I learnt a lot."
The visit was part of Cameron's three-day trip to India. While in Amritsar, he laid a wreath at the memorial to the 1919 Amritsar massacre.
Hundreds of unarmed people were killed by British troops in an attack described by Winston Churchill as "monstrous".
Soldiers led by Brig Gen Reginald Dyer fired on thousands of peaceful protestors and did not stop until their ammunition ran out.
Cameron wrote in the book of condolence but did not apologise for the atrocity. He said the event was "deeply shameful" but said it would be wrong to say sorry for the crimes committed during British colonialism.
In the book, he wrote: "This was a deeply shameful event in British history, one that Winston Churchill rightly described at the time as 'monstrous'.
"We must never forget what happened here, and in remembering we must ensure that the United Kingdom stands up for the right of peaceful protest around the world."
However, relatives of those who died criticised Cameron's decision not to issue an apology.
Sunil Kapoor, whose great-grandfather died, said: "If you feel shameful then why not make an apology?"