This may likely have been the hideout to which Morgana took the wounded Morgause and where she was taught magic. Morgana revealed the location of her hut to Agravaine, and that's where he went to inform her of the events that occured in Camelot (The Darkest Hour, The Wicked Day).
In the episode A Servant of Two Masters it was revealed that Morgana's hovel lies in the Valley of the Fallen Kings. She had become the leader of the bandits that infested this area and set a trap, thanks to the information Agravaine had given her, for King Arthur and the Knights of the Round Table. Anyway, they all escaped, except Merlin. When the young warlock came to her home, disguised as Old Merlin or "Dragoon the Great", to kill the Fomorroh that was controlling him, the two engaged in a magical battle that partly destroyed the interior of the hut (A Servant of Two Masters).
After Morgana was badly wounded by Emrys, Agravaine stayed in her hovel and nursed her back to health (The Secret Sharer).
When the High Priestess used a magical coin to summon Lancelot's shade from the Spirit world through the Pool of Nemhain, Morgana took the knight to her hovel and there she told him everything he would have had to know to make everyone believe he was the real Lancelot (Lancelot du Lac).
When Morgana conquered Camelot again, she no longer needed her hovel (The Sword in the Stone).
It is currently unknown if, after Morgana escaped Camelot after her second overthrowal by Arthur and Merlin, she returned to her hovel.