Two teens in Paris are seeing the light after being trapped underground, lost among the bones in the catacombs.

The catacombs are part of the underground system that forms a web of 150 miles of tunnels beneath the City of Lights. They hold the bones of about six million people, the BBC reported.

The bones were transferred to the tunnels after the city's cemeteries filled during the 18th century.

Part of the catacombs are opened to the public, but most of it officially is barred off from public view. The barriers do not stop people from sneaking into the burial chambers to explore or hold parties, the BBC reported.

The two teens, ages 16 and 17, were found after dogs and rescue crews spent four hours combing the underground system. Officials said the teens went in Saturday, but they did not say how or when they were first alerted about the boys’ adventure.

The boys have been treated for hypothermia, since temperatures in the catacombs register at about 59 degrees Fahrenheit, the BBC reported.