It lies near Baltimore's workshop, far behind troll's lair. In the wreck, there is a chest containing Journal from the Eyla Tarn, Vran armor enhancement and some crafting components. Finding the journal will advance the Mystic River quest. Iorveth's path: You can always find the shipwreck, unlike Roche's path, there is no mist blocking access. Roche's path: You can find the wreck, and she-troll during your trip to Vergen during The Siege of Vergen.