Deepwallow is a small plantation with only a few residents. It is located within Dementia south of New Sheoth, northwest of The Howling Halls. The town is the starting point for the unmarked quest "Ghosts of the Hill of Suicides".
It is a crime in the Shivering Isles to commit suicide, the punishment for that poor soul is entirety trap on the Hill of Suicides. The only way to break the curse is if somebody is to return the skull to its spirit.