Read "Ennui" at The Eldritch Dark:
This sonnet from Clark Ashton Smith (CAS) was first published in the May 1936 issue of Weird Tales magazine, hidden behind a truly ugly cover painting from Margaret Brundage!
It seems to me that this poem describes a state of purgatory. The opening octet features imagery that is awash in suggestions of death:
Have stilled the fountain and have sealed the fountain-head
And pall-wise draped the pine and flowering myrtle-tree.
However, in the closing sestet, CAS makes it clear that the setting is somewhere between life and death:
Where Styx and Lethe fall; where skies of stagnant grey
With the grey stagnant waters meet and merge as one:
The River Styx is of course the legendary boundary between Earth and the underworld (Hades) originating with Greek mythology. Lethe is one of the five rivers within Hades itself. So I read "Ennui" as describing a journey that has crossed the Styx, but has not yet reached into the heart of Hades itself, thus a sort of purgatory.
That notion calls attention to the title, since ennui could well describe the mindset of one who has grown tired of mortal life, and is ready to chart a course to that which lies beyond that life.