The Voynich manuscript, a 500 year old book of strange and unclassifiable plant drawings and a text which has still not been deciphered.
From Yale’s Beinecke Rare Book Library (click for more!):
“Written in Central Europe at the end of the 15th or during the 16th century, the origin, language, and date of the Voynich Manuscript—named after the Polish-American antiquarian bookseller, Wilfrid M. Voynich, who acquired it in 1912—are still being debated as vigorously as its puzzling drawings and undeciphered text. Described as a magical or scientific text, nearly every page contains botanical, figurative, and scientific drawings of a provincial but lively character, drawn in ink with vibrant washes in various shades of green, brown, yellow, blue, and red.”
I’m gonna go out on a limb and say this has something to do with the code Ilan is trying to decipher.