Priest hole
From Tardis Wiki, the free Doctor Who reference
A priest hole was a room built in English Catholic homes during the late 16th century while Catholics were being legally persecuted.
Harney Hall had a priest hole. (AUDIO: The Devil's Armada)
When Roundheads and Royalists attacked each other in the village of Little Hodcombe in 1643, Will Chandler took refuge from the violence in a priest hole. (TV: The Awakening)
Clyde Langer and Luke Smith escape from the nuns at St Agnes Abbey using the priest hole tunnels. (PROSE: Eye of the Gorgon)