YSGARD

The Heroic Domains of Ysgard, also referred to as Gladsheim, was the GREAT WHEEL plane straddling the alignments of chaotic good and chaotic neutral. Like the Greek influence on ARBOREA, much of this plane was heavily dominated by the gods of the Norse pantheon who had little interaction with the other pantheons. 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.
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 gigantic 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.
YSGARD The name of this layer was also the name of the confederation of godly domains known as Asgard, home of the Norse pantheon, or Ysgard in the Norse tongue. Each realm was the size of a PRIME MATERIAL PLANE empire and they were drawn together by the proximity of YGGDRASIL. 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 SEA, much like the in the WORLD TREE cosmology. The usual color pools connecting Asgard to the ASTRAL SEA existed but were little used. Portals in the guise of wells connected this layer to the neighboring planes of ARBOREA, Limbo, and OUTLANDS. In addition to YGGDRASIL, the Norse gods controlled and carefully guarded a portal directly to the PRIME MATERIAL PLANE where they were the strongest, called the Bifrost or the rainbow bridge.
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.