

Make your way to the flooded valley (the large central body of water that the river runs into and out of). Use your Witcher Senses to find the footprints leading away - when they disappear, open your inventory and examine the Old Map of Toussaint that Yennefer included with her letter. Make your way to the cemetary and examine the ransacked grave at the base of the large tree.

The letter explains that there was a scientist researching Witcher mutations in Toussaint, and that Geralt should be able to find information in his grave.
