3 years before Last Crusade, set in 1327, this featured Sean Connery and Christian Slater finding secret passageways through catacombs into a labyrinthine hidden library with Escheresque stairways. Concealed buttons reveal stone steps, and there's even a "Word of God" style riddle:
Adso remembers how Salvatore said "tertius equi", which is Canis Latinicus for "The third of horse" (when he meant "the third horse"). William concludes: "the first and the seventh of the four" really means "the first and the seventh of the word four", and "four" is "quatuor" in Latin, so you have to push the letters Q and R!