Life in the Tunnels: Inside the Underground World of Bucharest, Romania's Sewer Kids

— -- Amid the traffic rolling through downtown Bucharest, the capital of Romania, every once in a while, just for a second, a face will pop up out of the sewer. Then, just as quickly as it appeared, the face vanishes, with few people ever noticing it was there.

Hundreds of people live in the tunnels of Bucharest's sewer system -- and it's not just adults, but children, too.

Watch the full story on "Nightline" tonight at 12:35 a.m. ET.

One such child is Robert, who said he has been living underground since he was 9 years old. He said he doesn't know his parents, and that the people he lives with in the tunnels are his family.

Now, an entire generation of children has grown up in the sewers. They fled underground in 1989 when the Communist regime was overthrown and Romanian orphanages were closed, releasing thousands of kids onto the streets. Many took refuge in the sewer tunnels, heated by steam pipes. They are lost boys and girls who have now grown into adults.

Above the tunnels on street level, an entirely different world thrives. There are restaurants, fancy cars, shops and government offices are nearby. Many of the sewer tunnels are stacked with garbage and rotting clothes serving as beds. A few have sleeping bags. The police have tried sealing the sewer entrances, but the tunnel people just find another way in.

Drug addicts also live in the tunnels, and it can be dangerous. To be allowed inside their world, Robert said, we would need permission from their leader, an elusive and mysterious man known as Bruce Lee.

Lee has lived in the sewers for the past 24 years, and he is treated like a king by those who live underground. He has silver hair, which he paints with aurolac -- a metallic paint popular on the streets as a cheap way to get high. He also wears jingling medals and keeps a large pack of dogs with him.

"Nightline" visited several tunnels looking for Lee and met many sewer dwellers. There are few services or opportunities for them. They have been down there so long that moving out is not something they discuss. A girl named Florentina told ABC News' Bob Woodruff that the tunnel where she lives is packed with people, with no more room for anyone else.

After two days of searching, we found Lee. Just as predicted, he was surrounded by a large pack of dogs and was wearing hundreds of medals.

Speaking in Romanian, Lee said children come to the tunnels because "they have nowhere to go, but here they have food and water and heat."

"I know them all," he added. "I control everything down here. They used to do a lot of bad things. They didn't have anyone to guide them to do good before me."

Lee said the tunnel people turn to drugs because it's a comfort to them, an escape from their harsh reality. With drugs, "you're not hungry, you're not thirsty," he said in Romanian.

The tunnel Lee lives in is different than others. His is lined with people sitting on hot pipes. It has electricity, a microwave, a fan, even a Christmas tree.

"We take it from the city. ... Everything we have we have collected from the garbage," Lee said. "This is how we can live. If not, we would die out on the streets."

"The tunnel runs for about 2 kilometers," he added. "There are a lot of kids down there at night. That's when they gather. During the day, they go and search in the trash for food or whatever they need."

To report this story, "Nightline" hit the streets with a charity group called Samu Social, the only organization in Romania working with the sewer people.