This page offers a guide on the Gullhild Altar mystery in Gullnámmar, in the Dawn of Ragnarök DLC.
This offering altar is found north of Sudra Mylna. It asks you for x5 Hare’s Feet.
How to Get a Hare’s Foot
Lucky for us, there are a bunch of Hares in the fields around the altar! They can be hard to spot and are also incredibly skittish, so try to move around slowly and use Odin’s Sight to find them in the grass. Your best bet is to use your bow and arrow as it’ll be near impossible to get near them with a melee weapon!
You should get one Hare’s Foot each Hare (not always the case though), so you should only have to kill around 5 or 6.
Once you have 5, return to the altar to earn yourself a Skill Point.