"A person can get lost and then simply disappear." Trafficked young girls are being "broken into prostitution" - and hidden from the law - behind a maze of passages and secret cells in crumbling brothels across New Delhi and other major cities, campaigners say.
They are led to small, windowless rooms and the doors are closed.
"Nothing in this place has changed since I was brought here 20 years ago," a sex worker said as she applied make-up and got ready for clients. The maze of rooms, the way deals are struck and the plight of the women stuck here is frozen in time." More and more survivor testimonies are providing evidence about brothel layouts and the extent of exploitation in them, spurring many agencies to push for their closure.
Pimps haggle with customers, older women solicit and younger ones watch quietly.
As exchanges are agreed, customers enter the brothels.
Many trafficked young girls end up on the congested streets of New Delhi's largest red light district, known as GB Road.
Dimly lit staircases, next to ground floor hardware stores, lead up to hundreds of multi-storied brothels.
Urgent action is needed." Hidden in bunkers When policeman Prabir Kumar Ball started investigating a missing persons complaint in India's eastern West Bengal state this year, he thought it was a routine case.
But the search for a teenage girl led him to the brothels of New Delhi and Agra, a popular tourist destination some 200 km (124 miles) south of the capital and home to Taj Mahal. Rescuing them was like going to war," he told the Thomson Reuters Foundation.
"We get specific tip-offs about children being brought here but when we come for rescue, we sometimes find no girls - they vanish." The government has introduced a number of measures to combat sex trafficking - from strengthening laws to boosting social welfare schemes.
But reports of young girls being sold for sex and hidden in labyrinths are rising, campaigners say.
It’s the oldest profession in the world and Kandapara brothel in Tangail is the oldest in the country.