Doorway Cave is a cave located near Calla Bryn Sturgis. It holds a magical door made of ghostwood. It also contains a near-bottomless pit. It used to be called the Cave of the Voices, but its name was changed when Black Thirteen and the Unfound Door arrive in the Callas.
Doorway Cave has the magical ability to read a person's mind, find their insecurities and fears, and project them as the voice of someone from the person's past.
In Wolves of the Calla, Mia escapes through the door after the defeat of the Wolves. Roland's ka-tet follows her through the door into New York City as well as traveling to Maine in order to get Calvin Tower to sell the vacant lot.