Where does Persephone spend a month of the year?

She spends it in Hades, the mythological underworld. She is the queen of this underworld, and she is forced to spend 3 months out of the year there as payment for eating the food of the dead, which cannot be consumed by the living. She ate three pomegranate seeds, so she spends 3 months. This is part of the tale of the origin of the seasons.