Witcher 3 Hidden From the World Quest Guide
Start Location: At an abandoned campsite, just to the east of the ‘Maruader’s Bridge’ fast travel marker.
At the abandoned campsite, look for a bandit, or a corpse. After defeating the bandit, or locating his corpse, loot the body for a Letter. Read the Letter item in the Key Items section of the inventory. This will trigger the ‘Hidden From the World’ side-quest.
Follow the new objective marker across the road to the south and to the top of a small hill. Kill any Nekkers that are lurking about this area. Once you are alone with nature, at the top of the hill, switch on Geralt’s Witcher Sense to locate the chest here.
Simply open the chest here to complete the side-quest. It contains a decent assortment of sellables and reagents for crafting.