Pandemonium

The Windswept Depths of Pandemonium is an outer plane slightly in the negative energy zone. It is a plane of pure madness and lunacy. The entire realm is a porous rock with miles upon miles of caves carved through it by the incessant wind. There is an endless whistling from the wind blowing through these caves, and that tends to drive creatures mad quickly. Most denizens of this plane cannot remember their identity or why they came to the realm in the first place. Survival in this place is a dismal prospect, having to rely on seeking shelter in the caves and finding the few nooks and corners where the wind is but a gentle whisper.

For more information on this plane, see the 5th Edition Dungeon Master's Guide, page 62, or the Forgotten Realms wiki: here.

The Storm's Redoubt

Among the dense rock and howling winds, the Olcrid god of storms, Haalvin, has crafted a fortress that stands as a bastion against the madness of the realm. Short and squat, this fortress is mostly sheltered against the wind, though it finds even the smallest crack in the masonry and whistles its way in. The wind noticeably swirls around the top-most floors of the fortress, where Haalvin has his residence, as he controls the weather and directs the storm.

Type

Dimensional plane