Among the many secrets that Baldur's Gate 3 there is an entire race of people, the Kuo-Toa, hidden away from the rest of society in a hole even deeper than the Underdark. The plot takes players through many hidden places but this one is so hidden that it's not labeled on the map and no markers will direct players to find it.

Where to Find the House of Grief in Baldur's Gate 3
The House of Grief is an important part of Shadowheart's story in Baldur's Gate 3.
The Festering Cove, therefore, is a special treat for those who stumble upon it. Some may even scour every map in Baldur's Gate 3 and never find it. Players will either need to get lucky when they wander around and spot this secret entrance or find out from the community.
Updated August 12th, 2024, by Kristy Ambrose: The Festering Cove was one of the many secrets discovered literally months after the Baldur's Gate 3's initial launch, and became one of the best examples of how detailed and creative everything in the game really was. It's these kinds of secrets and adventures that gave BG3 so many dedicated fans and famous awards. The realm of the Kuo-Tao feels unfinished, especially considering the level of detail for such a minor area that most players never see, but perhaps future updates will reveal more, or the location will appear again in the lore of the D&D universe.