Witcher 3 Shortcut Walkthrough
Start Location: On the island of Undvik – the large, southwestern island of the Skellege Isles. This can be found by a boat on the northern shore of the lake just to the west of the ‘Dorve Ruins’ and northeast of the ‘Urskar’ fast travel markers.
This location of interest will pop up as a Hidden Treasure marker as you get close. As you approach it, you’ll see that it is highlighting a small rowboat on the shore which is guarded by a group of three Bandits. Once you have cleared the area of the bad guys, use Geralt’s Witcher Sense to examine a bag of loot in the boat for a Torn piece of paper.
Read the Torn piece of paper in the Key Items section of the inventory. This will update our objectives and trigger the ‘Shortcut’ side-quest.
Make your way to the objective marker out in the water to the southeast of your current location. Here a search area will open up around a sunken ship (the mast should be visible above the water). Dive underwater and search the lakebed using Witcher Sense to find a glowing red chest.
Loot this chest here to complete the side-quest. It contains a 40 Florens, Runestones, some artefact armor and some crafting reagents.