Chernoggar is a Dominion within the Astral Sea of the World Axis cosmology of Dungeons & Dragons, which serves as the traditional home of the various Dawn War gods of war and battle. Originally the domain of the dead god Tuern, it was usurped by his murderous brother Achra, better known today as Bane - Achra didn't get long to enjoy his new holdings, however, as Gruumsh promptly decided that he wanted to take Achra's power for himself and smashed his Dominion of Nishrek into Chernoggar, binding the two realms together and beginning a war between the two deities and their faithful that has lasted every since.
In effect, Chernoggar is an homage to the 1st layer (and thus the most famous part of) Acheron, hosting as it does the eternal war between orcs and goblinoids. Chernoggar was the original homeland of the bladeling race, before they mostly abandoned it in anger at Bane's betrayal. Lesser gods known to serve as exarches of this realm include Maglubiyet under Bane, and Bahgtru, Luthic and Vaprak under Gruumsh.
Chernoggar is fully detailed in the 4e splatbook "The Plane Above: Secrets of the Astral Sea".
Chernoggar is, to put it bluntly, a real shithole of a place. Whilst neither it nor Nishrek were picnic spots to begin with, the violence of their fusion has really fucked the place up. Whilst the enormous Crash Peaks vaguely mark the scars of where the dominions crashed together in the first place, both territories have been conquered, lost and reconquered so many times that it's doubtful even Bane and Gruumsh can keep it straight who owned what to begin with. Volcanic peaks sprout across Chernoggar like mushrooms, and constant earthquakes rip open or seal shut gaping crevasses. Whilst some parts of the dominion burn with volcanic magma pits or are swept clean by the scouring touch of freezing winds, for the most part it's oppressive and depressing The rust-red sky hangs low over the land, and the weather always seems to linger past the point of being comfortable, whether it brings fog, wind, hail, or warmth, resulting in natives being short-tempered and distracted.
As the dominion of the war gods, it goes without saying that Chernoggar is a place marked by war. Fortresses, watchtowers, aeries, dungeon passes, patchwork redoubts, walls, battle trenches, ports and bunkers are absolutely everywhere; running through the dagger's edge of mountain ridgelines, rambling through bramble-choked valleys, and sinking into swamps so soaked in gore that the native life has adapted to being nourished by blood instead of water. A riverbed in Chernoggar will house more rusting arrowheads than stones.
Many who see Chernoggar for the first time wonder if they haven't accidentally stumbled into Baator somehow. Those who've actually seen the Nine Hells will usually swear that Chernoggar is better, as the dominion isn't without its own brutal beauty. At least each day in Chernoggar offers moments of triumph, and the slim chance of personal - or even cosmic - victory.
Major areas in Chernoggar consist of: The Stairs of Woe: The heavily fortified, mile-high cliffs that form the foundations of the plateau upon which Chernoggar sits. From the dry, barren lands surrounding the dominion once one leaves the Astral Sea, one has to ascend these steep and winding staircases, which run between an endless series of guard towers controlled by Bane's worshippers.
Tuer-Chern: The enormous fortress-metropolis that serves as the palace of Bane himself.
Tower of Skulls: The palace of Gruumsh, a tottering structure of skulls lashed together with chains and entrails that looms amidst volcanic peaks and clouds of acidic smoke.
Zoronor: The former homeland of the Bladelings, a bleak place that was once a port town and is now surrounded by deadly salt flats. It provides an alternative way to reach Chernoggar proper besides the Stairs of Woe, but the bladelings often just sell would-be customers to the arena in Clangor.
The Tower of the Adamantine Mage: The heavily fortified and trapped dwelling of Koth-Amar, a mad archmage who gained immortality by transferring his soul into a golem of solid adamantine. Serves as a storehouse for magic and knowledge plundered from across the planes.
Crash Peaks: The enormous peaks that mark where the two Dominions first slammed together, they have been so riddled with bridges, tunnels, trails, dungeons and other connections that the former barrier is now just another place to fight.
Climbing Caves: A series of ever-shifting, monster-infested caves on the Nishrek side of the dominion, which run from the surface of the dominion to the dry seabed at its borders. Both of the gods make use of these as a passageway to allow their troops to maneuver around the outside of their dominion, and fight a constant battle against each other, the native predators, and the shifting stone for control over the caverns.
Stone Sea: A series of vast badlands where the earth flows like water, writhing like the surface of the sea in the middle of an immense store. Bane and Gruumsh's forces carve enormous tors into rocky citadels that float across the roiling landscape, clashing in brutal battles.
Lakes of Lost Hope: The biggest bodies of water in the dominion, these inland seas are deadly, from the treacherous marshes, rushing rivers, broad quagmires and waterlogged jungles surrounding them to the hurricane-lashed, waterspout-riddled, turbulent, monster-infested bodies of water themselves.
Like all dominions within the Astral Sea, Chernoggar is surrounded by Border Isles - comparatively smaller mini-worlds that lie within its color veil, but which are not officially part of the dominion proper; this is the dumping ground for Outsiders, those souls who are condemned to never complete the transformation into Exalted and thus never set foot in the plane of their deities. Owing to the violent nature of Chernoggar, the Shrapnels are a mirror of that violence; the various islands sporadically slam into each other, resulting in them randomly fusing, sundering, or ricocheting, making it impossible to keep track of how many individual islands there are.
The Shrapnels are a gathering point for reavers, pirates and mercenaries, as well as all manner of monsters. Warlords come and go here, as if the plane itself rejects attempts by any one faction to grow too large; inevitably, a rising warlord is destroyed or sees his forces splinter - either to serve rivals from within his own ranks, or just out of fear of the ever-mounting attacks by planar predators. Racially, it's one of the biggest melting pots in the Astral Sea; outsiders of all species, from orcs and goblinoids to more conventional fare rub shoulders with renegade angels, rogue devils, bladelings and githyanki. Life here is tough; the only law is the law of the strong, enforced with blade or spell. Yet, much like Chernoggar itself, life flourishes here despite the strife, with forests and rivers springing up to recolonize each island as swiftly as it is damaged in the churning maelstrom.
A handful of Shrapnels have lasted long enough to earn a particular infamy amongst mappers of the Astral Sea:
The Isle of Rage is a blazing whirlwind of destruction, a volcanic-bedecked, flame-spewing meteorite that whirls quickly and erratically around Chernoggar's orbit, infested with blood-crazed fiery elementals and archons that seek to annihilate whatever comes near. It is said that the Isle marks the spot where Bane slew his brother, Tuern, and that the fiery god's heart still lies buried at the center of the Isle, which is why it sprang free when Nishrek slammed into Chernoggar so long ago.
Reaver's Haven is an island with particularly abundant veins of iron ore, which has made it a beacon for pirates, freebooters and mercenaries of all stripes, who carve out their fiefdoms amidst the readily-fortified caverns and hills.
The Gnashing Teeth are a cluster of three islands that always maintain a close orbit, constantly smashing into each other. Githyanki and bladelings fight for dominance here, seeking to capture the mighty defenses left from when the Teeth were a single island, fortified by the battlesworn of Bane.
Rimeval is an enormous mass of glaciers locked under an eternal blizzard. But, concealed within its icy depths are a god's ransom of astral diamonds, and strange treasures lost since time began. Rimeval is a place where anything that has cursed to be lost eventually comes to rest, and thus it draws a steady stream of desperate or fool-hardy adventurers.