After defeating the Sanctuary Guardian, you will end up in this Graveyard-like area containing only a loot-able corpse with 1 Humanity, Elizabeth, the only female mushroom-person, and a bonfire. She sells the spells of Oolacile and some other items and will ask you to save Dusk once again. If you succeed in your quest, she will reward you (visit her page for more details).
There won't be another bonfire for a while, after a field of relatively tough enemies and a difficult boss fight, so you may want to kindle this one. To the right of Elizabeth is a path to the next area, the Royal Woods.
Oolacile Sanctuary Map
(Work in progress)
NPCs in the area