You must first defeat the boss Valiant Gargoyle. After Valiant Gargoyle you can find the site of grace “Great Waterfall Basin” in the same area where the boss fight took place. In front of this is a stone coffin you can interact with that brings you to the Deeproot Depths. From where you spawn, follow the roots on the right side , leading to a cave with large ants. Always follow the left path in the cave. At the exit you find this spell.