The Hole (2001) http://www.imdb.com/title/tt0242527/
One misty morning, Liz Dunn stumbles down the road to her school and screams for help. A police psychologist gets her to reveal her story: A month earlier: three rebellious teenagers - Mike, Frankie and Geoff are trying to ditch the school field trip to Wales. The school nerd Martin helps them out by allowing them to stay in an old war bunker for the three days on the condition that his friend Liz joins them. The teens go down, party and have great fun but Martin doesn't return to let them out and they hope and pray that someone will find them...
Thora Birch ... Liz Dunn
Desmond Harrington ... Mike Steel
Daniel Brocklebank ... Martyn Taylor
Laurence Fox ... Geoff Bingham
Keira Knightley ... Frances 'Frankie' Almond Smith
Embeth Davidtz ... Dr. Philippa Horwood