Escape the Fury Ambush
Story related. Cannot be missed.
Will unlock in Chapter 20: The Gauntlet of Apollo.

At the end of Chapter 19 you will be ambushed by the two remaining Fury sisters, Alecto and Megaera. They attempt to lure Kratos in with more illusions but he resists and begins to fight. After fending off illusionary Spartan soldiers and a fury sister you will fight the second sister and her phoenix-like bird. Once you defeat her, both sisters will join the battle together for the final standoff. Defeat them both and a long cutscene will begin.