I once read a book about a group of people who discovered a hidden temple city in a mountain range, where the Incas-the ancient civilisation of Peru- had fled to when the spanish invaded. When this group found the burial chamber of one of the inca high priests, they unleashed a powerful curse upon them all...
This tome looks like a haphazard collection of random notes on different types of paper stitched together and bound within a wooden cover. The pages describe all of the 300,000 gods of the world, each in the language of the people who worship them. The book is stored high in the mountains, kept safe by an order of monks. Reading the entire book confers a deep understanding on the nature of the cosmos and access to incredible power. This only works, however, if it is read without translation, meaning that the reader must master each language contained within. The various monks know these languages but there is typically only one alive at a time who knows them all. This monk would be an excellent source of information and/or magic. IF the PCs learn about it; IF they can find the monastery; IF they can convince the monks to help them; AND if they can understand the convoluted riddle given as an answer.