The Book of Thoth may be discovered at any time, or, maybe it already has been, but was too damaged to be recognized. Many fake books of spells are attributed to Thoth. If any of these show how to understand the speech of animals and to see the gods themselves, then it’s the actual book of Thoth. There are so many books that claim to be written by Thoth that the real one may take forever to identify, or maybe it’s more hidden than Koschei’s needle.
Impossible objects