Danuwar tried refusing, but says a man who guarded the place came up to her with a long knife and threatened, "If you don't do this work, I'll cut you up and throw you on the street like a stray dog." She was soon sold to another brothel where the owner forced her to line up with the other girls -- "there were 40 of them, the youngest about nine" -- to have sex with up to 30 clients a day. When she tried to say no, the men would often burn her with cigarettes. Running away was impossible; the girls were paid nothing and constantly under watch.

"Nepal is particularly bad right now," says Taina Bien-Aimé, the former president of Equality Now, which advocates for women's rights around the world. "It's extremely poor and these girls are prized for their fair skin in India. Most important, they are just not valued by the culture. Their families figure: I can marry her at 12 for a cow, or sell her to a trafficker -- what's the difference?"

According to the U.S. State Department, thousands of Nepali women and children are trafficked to Indian brothels every year. In 2007, Nepal enacted new laws that prohibit and punish trafficking. However, implementing those laws has been far more difficult. Nepal and India currently share an open border, which has been a goldmine for traffickers who smuggle women out of Nepal and into the Indian brothels where they are sold for as little as a few hundred dollars.

Danuwar was finally freed at age 16 in a police raid. In 1997, she helped found Shakti Samuha, which in Nepalese means, "the group that empowers." The organization is run by Danuwar and other survivors of sex trafficking. Shakti Samuha provides returning sex slaves with a safe haven, psychological counseling, education, and training for jobs like barista, seamstress, or beautician. Danuwar operates from a shelter on a dirt road across from a massive garbage dump in Kathmandu, Nepal. When I visited, one room in the shelter was filled with women learning to sew amid piles of donated potatoes.

Laxmi Bishwokarma, who worked in an Indian brothel, is one of those women. She spends most of her days sewing colorful outfits inside the dark, cold room so she doesn't have to go back to her old job. Bishwokarma was trafficked to India and sold into prostitution by her uncle when she was only 15.

"On a quiet day I would have to sleep with 30 to 35 people in the brothel. On a busier day, I would have to sleep with about 70 to 80 people," Bishwokarma told me, sitting on the rooftop of the shelter wearing a green-stripped sweater with her hair pulled back in a ponytail.

"When I didn't want to have sex, they would beat me," she says.

Traffickers often use promises of a job to lure thousands of Nepali girls out of their homes in remote villages and thrust them into the booming sex industry of India. "We were told we were being sent to Lebanon. But they took us to the brothel," says Bishwokarma. Often, traffickers will target girls who are uneducated and come from lower castes.