Morgause's Cave

Morgause's cave is located near or in the Darkling woods in the kingdom of Camelot.

The cave was guarded by the Blood Guards, and might be the place where they hid themselves, thus surviving the Great Purge.

It's possible that the cave is also where Morgana spent a year, recovering from hemlock poisoning and learning how to control her powers, under the guidance of her half-sister Morgause. This may have also been where Morgause moved to after Arthur and Merlin went to her ruined castle, or it could just be a useful hideout for Morgause, close enough for Morgana to come and go from Camelot without her absence being noticed.

In this cave, Morgause prepared a potion in a big cauldron in which she threw a handkerchief, which had Uther's tears on it and a Mandrake root, that sank in the potion. The spell caused Uther to hallucinate, seeing people who had died because of his choices and actions before and during the Great Purge.

It's unknown whether, after the events in The Tears of Uther Pendragon, Morgause stayed in this cave, or went to Cenred's kingdom with Cenred, or to another hideout of the High Priestesses.