This mystery can be found in the northwest of Jotunheim, in the easternmost part of Utgard. You’ll need to find a house built into the rock, marked by three red banners outside. Once inside, make your way to the back of the house as it opens up into a fighting pit.
When you enter the fighting pit you’ll find a Jotnar named Dugr the Bold. He’s looking for a fighting partner, but no one else seems to want to join him. When you agree to join him in the pit, he will ask you to choose what form he should take, since he’s a shapeshifter. You can choose between a wolf, a lynx, or a bear, but regardless of what you choose Dugr will only be able to shapeshift into a rabbit.
When the fight begins, you’ll need to defeat a bear and a lynx, but you can only use your fists to fight. Both of the animals will behave as they normally would in the wild, so you can expect swift strikes from the lynx and heavy, cumbersome blows from the bear. As ever, look out for any attacks initiated with a red rune aura or an orange aura, and dodge out of the way where necessary. You can then follow the dodge with a series of light and heavy attacks while flanking the animals. This will be a relatively easy fight.
When the fight is over you’ll be speaking with Dugr again. He’ll provide you with a document containing vague clues to the location of two wealth chests. The mystery will complete after the conversation.