Ysgard

Gladsheim, also referred to as Ysgard, was the Great Wheel plane straddling the alignments of chaotic good and chaotic neutral. Like the Greek influence on Olympus/Arvandor, much of this plane was heavily dominated by the gods of the Norse pantheon who had little interaction with the people of Toril. The primary exception was Tyr, the Norse god of war and law who became known and widely worshiped as the God of Justice in the Forgotten Realms.

Some characteristics of this plane were ascribed to the World Tree cosmology planes of Arvandor, Brightwater, Gates of the Moon, and Jotunheim when that cosmology model became popular. When the Spellplague hit the cosmos, Brightwater merged with the Gates of the Moon which survived, along with Arvandor. Jotunheim was cast into the Elemental Chaos but only parts of it survived as described by the World Axis cosmology model.

Description
The three layers of Gladsheim consisted of tremendous rivers of earth and stone that formed cosmic arches through the void, like very tightly packed asteroid belts. Millions of miles/kilometers wide, each river was made up of Brobdingnagian chunks of matter that bumped and ground against each other at a glacial but noticeable pace, raising up mountains and opening vast chasms. These "earthbergs" all shared the same gravity field and most were inhabitable on the top side while the underside of the rivers burned with a radiant fire that provided a ruddy light to the rivers below. Earthquakes and landslides were a commonly occurring danger in Gladsheim as the landscape slowly buckled and broke under the influence of chaos.

Asgard
The name of this layer was also the name of the confederation of godly domains known as Asgard, home of the Norse pantheon. Each realm was the size of a Prime plane empire and they were drawn together by the proximity of Yggdrasil the World Ash. Like Mount Olympus, Yggdrasil was a multiplanar conduit connecting Gladsheim directly to Niflheim in Hades and Alternate Prime Material Planes without passing through the Astral Plane, much like the World Tree in the World Tree cosmology. The usual color pools connecting Asgard to the Astral Plane existed but were little used. Portals in the guise of wells connected this layer to the neighboring planes of Olympus/Arvandor, Limbo, and Concordant Opposition. In addition to Yggdrasil, the Norse gods controlled and carefully guarded a portal directly to the Prime plane where they were the strongest, called the Bifrost or the rainbow bridge.

Other known realms adjacent to Asgard were Vanaheim (home of the Vanir, beings of the air), Alfheim (fairyland, known for its chaotic elven spirits), and Jotenheim (home of the giants).

Muspelheim
The earthbergs of this layer were reversed (or alternatively, gravity was reversed) so the flaming side was up and the earthen side down. Surtur and the fire giants made their home here and guarded the barriers that lead to Asgard and its neighboring realms.

Nidavellir
The rivers of earth were in such close proximity in this layer that the entire sky was filled with fire, making it appear to travelers that they were in underground caverns and passages with a river of fire for a ceiling.

Inhabitants
Hollyphants and planetars were fairly plentiful in Gladsheim but many of the other Upper plane regulars avoided it. Wildlife included bears, wild boars, stags and other woodland creatures, all bigger and tougher than their Prime plane counterparts. Giants of all kinds lived mostly in Jotunheim but could be encountered just about anywhere. The giants of Gladsheim were generally more intelligent and better equipped (with giant-sized magic weapons) than those found on the Prime Material Plane. Some were accomplished clerics and mages, and illusionists who could even fool the gods.

Realms

 * Aerdrie Faenya, Seldarine Goddess of Air and Weather, had no permanent realm here but wandered among the layers of Gladsheim and Olympus/Arvandor accompanied by dozens of huge birds.
 * Bast, the Mulhorandi patron of cats and goddess of hedonistic pleasure, had a realm across the sea from Asgard in a vine-covered acropolis on the edge of a desert. Bast later absorbed the essence of a minor elven goddess, became known as Sharess, and moved to Brightwater.
 * Selûne, Our Lady of Silver, once made her home in Gladsheim before moving the the Gates of the Moon.
 * Surtur, king of the fire giants, had a vast realm in Muspelheim with outposts in Jotunheim.
 * Thrym, king of the frost giants, had his frozen realm in Jotunheim.
 * Tyr Grimjaws, the Even-Handed, once made his home in Valhalla, a realm in Asgard. He has only been known in the Realms for the past thousand years or so, and was widely believed to reside in the Seven Heavens at that time.