Witcher 3 Ruins, Hidden Treasure, You Know Walkthrough
Start Location: On the island of Undvik – the large, southwestern island of the Skellege Isles. This can be found by the ‘Dorve Ruins’ fast travel marker.
From the ‘Dorve Ruins’ fast travel marker enter the stone archway/gate and as you do, switch on Geralt’s Witcher Sense and look to the left (north). On the ground, here you should be able to spot a corpse which we can investigate.
Upon looting the body you’ll receive a Mysterious Map and an Old Key. Read the Mysterious Map item in the Key Items section of the inventory. This will trigger the ‘Ruins, Hidden Treasure, You Know…’ side-quest.
From the ruined town of Dorve, make your way to the ruined tower over to the east indicated by the objective marker. Kill the pair of Sirens who are flying around nearby before entering the tower. Climb the ladder inside to locate a chest by a harpy nest.
Loot this chest here to complete the side-quest. It contains a sum of Orens, and some other goodies.