Antagarich
Antagarich is the continent on which most of the action in Heroes 3 and its expansions take place. It is located on the world of Enroth.
History
Most of Antagarich was once ruled by the Wizard-Kings of Bracaduun. A legendary Barbarian, Jarg, united all the tribes of the Wastelands (Krewlod) and conquered the entire southern-half of Antagarich. However, after he died of old age, his heirs squabbled for the throne and dismantled the nation in their squabbles, allowing the Wizard-Kings to rise again and reestablish their empire. They oppressed Barbarian culture especially, attempting to suppress the history and legend of Jarg in fear that heroes would try emulating Jarg; and had nearly succeeded in that task when Tarnum rebelled and repeated history.
Tarnum, however, was not as wise as Jarg. His reign was especially ruthless and brutal, forever twisting Barbarian culture, and Tarnum himself turned out to be as much a tyrant as the Wizard-Kings were. Rion Gryphonheart would soon lead an uprising against the Barbarian King, and vanquish him in single combat. With Tarnum's death, his empire crumbled quickly, allowing Rion Gryphonheart to create the new nation of Erathia which quickly dominated most of the continent.
Nations
Mainland:
Erathia is the largest nation and occupies a central position. It shares borders with every other nation on the continent.
AvLee is the northernmost nation, and shares borders with Deyja, Eeofol, and Erathia.
Bracada is the southernmost nation, and shares borders with Erathia and Krewlod.
Eeofol is on the East coast, facing the Nighon Strait, and shares borders with Erathia and AvLee.
Deyja is landlocked, surrounded by Erathia to its South and West, and Avlee to its North and East.
Krewlod is on the western coast, between Erathia and Bracada.
Tatalia is on the western coast, facing Vori, and sharing borders only with Erathia.- The Contested Lands are on the border between Erathia and AvLee, near Eeofol.
Surrounding Islands:
Vori on the North-West. This island is permanently shrouded in supernatural cold (due to the Sword of Frost).
Nighon on the South-East. However, Nighon's subterranean domain extends far beyond its island of origin, stretching under the sea and reaching into the underground of Erathia, Eeofol, and AvLee.- Evenmorn on the South (under Erathian rule by the end of the world).
During the events of Armageddon's Blade, 
Conflux towns appear throughout Antagarich.
Geography
The following is a short story that was written by a New World Computing employee and published on the now-defunct fansite "The Nether Gods".
Let's start with some geography. Again, this is not my specialty, but I will give it a go. From the Erathian coast, a safe journey to Castle Ironfist in Enroth lasts approximately eight weeks. The travel time can be cut to six weeks, but the more direct route takes you dangerously close to the southern shores of Regna, where pirates lurk along the shipping lanes, disrupting most traffic. Regna lies to the northwest of Erathia, and Enroth to the west of Regna.
The Dungeon Overlords rule the eastern shores of the Erathian continent, as well as the Nighon islands off the coast. It is a broken land, but riddled with caves and underground passages - a perfect space for the dwellings of the eyeless troglodytes and other creatures of the dark. As for a Cult of Baa, I'm afraid I've never heard of it. Perhaps they are sheepherders?
The Stronghold nation of Krewlod lies along the western coast of Erathia, in the foothills between the Bracada Highlands (home of the Wizards) and the Tatalian Lowlands (where Xanthor and I traveled several weeks ago). They have always remained neutral in the affairs of Erathia.
Finally, you asked about the Temples of the Sun and the Moon. While there were a few temples of these religions, most were destroyed when the two went to war, leaving only remnants of each. Most stay in their homeland of Karigor, and are rarely seen here in Erathia.
Well, that should be enough for today. I will gather more questions and answer them tomorrow."Trivia
Antagarich is sometimes spelled "Antagrich" in official documents such as the Shadow of Death manual, notably in the description of the Pixies and Sprites, Halflings, Rogues, and Trolls. Greg Fulton coined the name "Antagarich" as a portmanteau of "antagonism" and "rich", connected with an 'a' to make pronunciation easier. A continent rich in antagonism...
References
- Gregory Fulton on Names in Heroes of Might and Magic III, Celestial Heavens forums, 8 August 2023.