JOLIET, Ill.  — A teenage girl who slipped into an abandoned Illinois prison for an urban adventure ended up serving a short sentence when she accidentally locked herself inside a cell.

Illinois State Police say two teenage girls entered the Joliet Correctional Center through a hole in its fence Monday.

Joliet Fire Department Battalion Chief Mike Stromberg says the teens were exploring the suburban Chicago prison that’s been closed since 2002 when one of them locked herself inside a cell.

The other girl got firefighters to the site, and they used a sledgehammer to break through a brick wall and free her companion.

Stromberg tells The (Joliet) Herald-News that she spent 45 minutes in the cell.

State Police say the teens will face trespassing charges.