I explored the large area called the Temple Steppes and found a locked golden chest. I'm guessing there is a large champion I need to kill in order to get the key but I can't seem to find it. I've looked all over the map and had no luck. Is this a bug? Is the key somewhere else? Did I really just miss the champion?
Find an enemy called Bittersprite on the same map as the Locked Golden Chest. Bittersprite looks like a large wasp or hornet. It is not necessarily near the chest, it can be anywhere on the map. You can see it floating in the top-right area of this screenshot:
Kill the Bittersprite and it will drop a Golden Key. The key will not appear in your inventory when you pick it up, but in the top-right corner of the screen it will say -You Found- and show a picture of the key. You can now open the Locked Golden Chest.