Cania, the Eighth Hell.

Both pre- and post-Spellplague cosmologies agree that Cania] was a bitterly cold-dominant realm of solid ice mountains, titanic, unnaturally fast-moving glaciers, and nearly continuous snowfall that made Stygia seem balmy by comparison. Unprotected travelers were exposed to temperatures of −60 ℉ (−51 ℃)[ but on the positive side there were few creatures that hunted in the icy wastes.
Earlier lore described the great citadel Mephistar as being constructed of iron but later reports say the Lord of the Eighth's fortress/palace was made of ice. All accounts seemed to agree the tower had a heated, luxurious interior and sat atop a gargantuan glacier called Nargus whose speed and movement were under the control of Mephistopheles himself.

Location under

Outer Plane - Nine Hells