Well done! You've found one end of the secret tunnel out of the
castle. The codeword is SALT.
Do you know where the other end is?
There's a secret passage into
Nottingham Castle. It's called Mortimer's Hole because on October
19th 1330 supporters of Edward III crept through a tunnel into the castle
and captured Roger Mortimer, Earl of March. Mortimer and the young king's
mother Queen Isabella had been ruling the country and their capture enabled
Edward to gain control. It is not certain, however, if this is the actual
tunnel used by the conspirators.