Demeter's October festival ("only for women who were especially purified")
"They reenacted Persephone's descent into Hades by descending into crevices in the earth (or artificial crypts)" [!]
Engelsman, 51
since it came in the fall, it "probably began as [a feast] of thanksgiving for the new grain" (55) but it (and the Eleusis festival) are "ultimately unique, [and] require a very special explanation " (Engelsman quoting Eranos-Jahrbuch here)