Among the many secrets that Baldur's Gate 3 holds is an entire race of people, the Kuo-Toa, hidden away from the rest of society. 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.
Baldur's Gate 3: Where To Find The Kuo-Toa (The Festering Cove)
There is a whole race called the Kuo-Toa that can go completely undiscovered in Baldur's Gate 3 unless players find a secret entrance.