This page will offer a guide on where to locate and how to complete the mystery, The Dreamwalking Warrior, in Rygjafylke.
Follow Eyvind the Sleepwalker
When you find Eyvind the sleepwalker, you’ll need to interact with him by pressing ‘E’. He will then begin sleepwalking towards the cliff with the rope zipline. You cannot stop him from walking and you cannot attack him or wake him up. Instead, you’ll need to follow him down towards the cliff and use the rope zipline after him.
When he reaches the bottom of the zipline, Eyvind will wake up. Speak to him to complete the Mystery and earn some EXP.