Tinker, Hunter, Soldier, Spy The Witcher 3 Guide
Last update: 11 May 2016
Northwest from Winespring Grange (M1,12), in the territory east from Novigrad, you can find an abandoned place with a guard tower. Walk on it and you will find a body and a letter and key next to it.
The clues will lead you to the nearby pond south from the tower. Near the pier, underwater you will find a hidden chest containing valuable alchemy ingredients and 200 florens.