(( Suggestion ))

A richly decorated book cover with obscure writing in swirling letters. The book has drawings and diagrams in the Egyptian style (( which to an expert eye would appear forged because of details got wrong due to ages of copying before it went in the treasure )).

If one were able to decipher the text, one would find stories on the powers of King Solomon, who commanded demons to build his temples. It would still remain to be seen how much of this is usable, but the right party would definitely be interested in such a historic tome.

(( Inspired by https://en.m.wikipedia.org/wiki/Testament_of_Solomon)) ))