In 1345 he personally discovered a collection of Cicero's letters not previously known to have existed, the collection Epistulae ad Atticum, in the Chapter Library (Biblioteca Capitolare) of Verona Cathedral

So basically a guy goes into a library, rummages for a while, and finds ~1400 years old text no one knew was there

Do we still have places that store texts (like libraries, but doesn't have to strictly be a library) where we don't have everything catalogued and we don't know what might be inside?