Be it the library of the local College of Magic or the study of that wizened old wizard who lives down the road, there will be a pile of tomes around... who knows, you might even be lucky enough to get to browse through them.
So of course you ask what you've picked up to leaf through... and the GM has a sudden blind moment of panic. But fear not, if said GM has this in possession, it is but a moment with the percentage dice to tell you that you have a pristine copy of Le Grand Arcane, ou l’Occultisme Dévoilé (1868) by Eliphas Levi in your hands. Or maybe a battered and annotated volume entitled Cantus Circaeus (or the Incantation of Circe)
(1591) by Giordano Bruno.
Use as is if you are running, say, Call of Cthulhu - you might want to change dates and maybe some of the author names (what, you didn't recognise Giordano Bruno? OK, leave that in, then!) to fit your particular setting.
A fine selection to conjure with... or maybe go mad... and some of them at least are really out there...