The Cartographer's Blank Page
Invisible ink puzzle
Hard
By
Bookwyrm
A soot-dark page torn from a map-maker's notebook, apparently empty.
The Guild of Cartographers marks its secret routes in fluorescent ink that only shows under a lens of violet glass. The page looks blank. Its secret fades again the moment the light moves on, so the party has to piece it together.
The page is blank, but it has been handled far too often for a blank page.