Annwyn/ Tir na Marbh
Annwyn is the Welsh underworld of which not much is known other than it is connected to the Irish underworld.
Tir na Marbh is the Irish underworld where The Morrigan rules over the three castes of the Irish dead. It is here she also rules over the Unseelie Court from her castle The Veiled Court.
The countryside of Tir na Marbh reflects an eternal Autumn on the cusp of Winter. Golden leaves hang from eternal forests while a chill air carries the scent of harvests and feasts at fair-time.
Somewhere within Tir na Marbh is a giant chain that stretches off through the eternal void and connects to Mag Mell.