As the air-conditioned bus weaves through the bustling traffic of the eastern Indian city of Kolkata, tour leader Sujoy Sen lists the many sights on the itinerary.

It sounds like a snapshot of the city's cosmopolitan history - colonial buildings like the General Post Office and the former British viceroy's mansion, Hindu and Jain temples, Greek Orthodox and Portuguese churches, an Anglican cathedral, the homes of freedom fighters who fought the British Raj and Indian merchants who prospered under it.

But unlike most heritage tours, this one happens after sundown. And its main focus is not just the history or architecture but the lights illuminating the buildings.

Kolkata Illumination Project is the latest addition to the city's many heritage tours and walks. Mr Sen, who runs a tour company, chanced upon a newspaper article about city enthusiasts lighting up some of the city's grand but often neglected heritage buildings. He obtained a list of buildings and went to check them out.

"I was stunned," he says. "I have seen Paris by night. I didn't realise Kolkata could be like that also. I wanted other people to see it as well."

Himanjali Sankar, born and raised in Kolkata, now living in Delhi, joined the tour. She says the buildings themselves are familiar to her but the illumination changes them. "It is like they are coming alive, reclaiming their grandeur."

The project is the brainchild of a citizens' group called Kolkata Restorers.

"But it's not a real organisation. There is no committee, no president. It's just a label. A WhatsApp group," says Mudar Patherya, the force behind the endeavour.

He says he didn't start out with plans to light up the city. He came upon an old market crowned with a grand dome and a broken clock that had numerals in Bengali, the language most commonly spoken in the city. An avowed Kolkata........

© BBC