There are Nine Valkyries hidden in Midgard and other realms that you have to seek out and defeat. When you are back to where you are supposed to be prior to seeing the ending, several things will open up that will allow you to continue and finish side quests or embark on a new one. Right after Kratos and Atreus finish their journey, the game will not end, though the credits will be rolling. Unlike in previous God of War games where after the credits rolled, you are left with nothing to do, the newest installment of God of War is much different.