God of War Ragnarok is teeming with optional objectives that span across multiple realms, but one of the earliest you're likely to come across is a quest (known as a Favor here) that tasks you with seeking out Draugr Holes. Each of these spawns a boss called The Hateful that you must destroy to close the hole, and you'll receive a Chaos Spark for each one you defeat. When you've closed all six holes, you'll combine the Chaos Sparks into a Chaos Flame, which can be used to upgrade your Blades of Chaos.
There are only six Draugr Holes to find in the game, but they unveil themselves rather slowly throughout your adventure, so you're not likely to wrap this quest up until fairly late in the game. They're all fairly easy to spot as you make your way through each realm, but if you've missed a few along the way, we've got the locations of all six Draugr Holes for you below.