Sail to the location marked on the map to find an opening in the rocks. Lower yourself to pass through and get out on the shore. Head right to find the Nornir Chest. Go straight from the chest to find the first switch beyond a geyser. Use your axe to freeze the geyser and hit the...
Each Nornir Chest gives you 1 Apple of Idunn (Health Upgrade) or Horn of Blood Mead (Rage Upgrade). This makes them one of the most useful collectibles in the game because they increase your two main stats. Especially on higher difficulties you should get all of them as early as possible...