First find your priest-hole
My knowledge of priest-holes - hiding places used from the 16th century onward to hide Catholic priests in Protestant England, as well as Cavaliers, Roundheads and the odd Jacobite and, one suspects, plenty of clandestine lovers - comes chiefly from Jean Plaidy, which means it dates back a way.
But now I can update it: from the 18th-century email list, Secret Chambers and Hiding Places, by Allan Fea, on the net. He notes:
From Horace Walpole, Mrs. Radcliffe, Scott, Victor Hugo, Dumas, Lytton, Ainsworth, Le Fanu, and Mrs. Henry Wood, down to the latest up-to-date novelists of to-day, the secret chamber (an ingenious necessity of the "good old times") has afforded invaluable "property"—indeed, in many instances the whole vitality of a plot is, like its ingenious opening, hinged upon the masked wall, behind which lay concealed what hidden mysteries, what undreamed-of revelations! The thread of the story, like Fair Rosamond's silken clue, leads up to and at length reveals the buried secret, and (unlike the above comparison in this instance) all ends happily!
Thank you Gutenberg Project!