This is Lewig's book. I found it at the mother's house. Lewig was a Druid. His writings narrate facts that took place in the 5th century. No matter the details, but he talks about the map of the worlds of the Sidh. A map drawn with a magic ink that makes it invisible! Therefore, we cannot read it, except if we possess the stone of Gaeldenn. It is holed in its middle and it should be used as a magnifying glass. With this stone, the ink appears to you.