The school's Head of History, Susan Casey, says it is a remarkable find.
She is hoping money can be raised to conserve the shelter and turning it into a teaching facility.
More top news
A new personalised cancer treatment and research centre, funded by the Sir Bobby Robson Foundation is to open in Newcastle.
Actor Rodney Bewes has died aged 79. The star is best known for his role as Bob Ferris in Geordie sitcom The Likely Lads.
A look ahead at the forecast for the Tyne Tees region.