Mountains of Mourn
It is one of the most dangerous places in the world outside of the Chaos Wastes. Not only is every animal extremely deadly, the landscape is also very unstable and sometimes even sentient. As a matter of fact, the Ogres are probably the safest thing in the mountains, because you probably have to hire some as bodyguards if you want to survive a trip there.
Most people who go there are traders attempting to cross the Ivory Road over into Cathay (which has become safer ever since Greasus Goldtooth taught the Ogres that tolling the caravans is more profitable than eating them), although a few Dwarf expeditions have built Karaks there (most of which have been eaten by Ogres) due to rumors of a mountain made of solid gold.
Places in the Mountains of Mourn
Ancient Giant Lands
In the eastern edge of the Mountains of Mourn are its tallest peaks. There the Sky-Titans of old dwelt in magnificent sky castles, only descending to tend to their herds of Mammoths. When the Ogres first migrated from their homelands in Cathay, they ended up in the Ancient Giant Lands first and thus began a campaign to kill and eat all the Sky-Titans. After rendering that race nearly extinct, they tore down all the sky castles too to add insult to injury. Nowadays its relatively uninhabited, only really visited by Ogres looking for Ironblaster cannons or travellers trying to pass their way through the mountains to visit Cathay or the Great Maw.
The second most holy place to the Ogres other than the Great Maw itself, the Fire Mouth is the largest volcano in the Mountains of Mourn. The Ogres worship it as the bastard son of the Great Maw and the Sun, and have their own cult dedicated to it known as the Firebellies.
Mount Thug is the most dangerous mountain to climb in the Mountains of Mourn, to the point where the Ogres believe it to have its own malicious sentience. As such, the act of climbing Mount Thug is essentially the ultimate Ogre test of manliness.
The Granitetooth Graveyard
Every Stonehorn is doomed to slowly turn into stone as they die of old age. When this happens, they go to one of several "Stonehorn graveyards" to die, the Granitetooth Graveyard being the largest. Travelers sometimes come to this place as Stonehorns are known to contain precious gems within their stone skeletons. However, many of them find that some Stonehorns haven't fully become statues yet, and they don't like having their final moments interrupted...
Wildlife of the Mountains of Mourn
We know a lot about the native animals of the Mountains of Mourn, mainly because the Ogre Kingdoms army list includes a lot of them. Most of them are based on extinct megafauna from the Ice Age.
Some of the most belligerent creatures in the Mountains of Mourn, with a habit of headbutting anything that doesn't look like a Stonehorn (and a lot of things that do). Has a diet of rock that turns their skeleton into stone, making them especially dead 'ard. The Ogres have learned the only way to dominate and tame them is to gouge out their eye, which is an especially traumatic experience for a Stonehorn because its typically the first time it ever feels pain in its entire life.
The Thundertusk are highly magical creatures resembling a trunkless elephant. They have the ability to gather the winds of magic between their tusks and use it to fire a frost blast at any threat or prey. The most famous Thundertusk who ever lived is Fridge, who accompanied a band of Ogre mercenaries as they traveled through the Empire and resulted in the coining of the word "fridgerated" to describe preserving meat with ice.
Although vultures are normally scavengers, in the Mountains of Mourn damn near everything is a predator so these guys don't mind food that isn't quite dead yet. Often tamed by Ogre hunters for the purposes of falconry.
Like sabre-toothed tigers if their sabre teeth grew from their bottom jaw.
Described as a combination of a Rhinox and a Sabretusk, these creatures are the standard Ogre cavalry.
Wooly rhinos. Young Rhinox are used as beasts of burden or to pull Scraplauncher and Ironblaster artillery, but fully grown adults are too stubborn to be put to labor. A few Ogres, mainly from the Ironskin tribe, have managed to tame adult Rhinoxen as cavalry, but these units are far more rare and more elite than Mournfang riders.
Proof Games Workshop was renaming mythical creatures for copyright reasons before Age of Sigmar gave us "Aelves" and "Orruks". The Yhetees are believed to originally be Ogres who stayed in the Ancient Giant Lands and mutated due to too much warpstone dust in the atmosphere.