The Emerald Hills

Ah, the Emerald Hills, such a lovely vista to look over. Visit you say? Gods no! I have it on good authority that dragons refuse to land there, and any place dragons consider dangerous is best left well enough alone.

— Jasper Cameron, Leader of The Bronze Ravens

It is a bit of a cosmic joke, I think, that the name "The Emerald Hills" is the one that stuck on the world maps. Just goes to show how important the look of a place is. If one is only concerned about looks then it is one of the best named places in the world. Bordered on three sides by steep granite slopes of the Myrskyt Mountains the rolling hills almost shine in their vitality. One cant be blamed for thinking "here would be a wonderful place to settle, for the land is fertile and protected, the winters are mild, the summers warmth is tempered by the elevation."
In centuries past you may even go as far as to approach a king or some other patron to fund a settlement in the area. After all, down the slopes to the east and a little north you enter the Viidakko Rainforest, so wood should be easy enough to come by. And sure, all but the most desperate of dwarven craftsmen may turn you down, but you are sure they will come around once your town is good and established. So, wagons loaded and livestock in tow, you set off... never to be heard from again.

The Fort of Burning Elk

The sheer number of disappearances as described above is the reason that some 600 years ago the various powers that be around the Myrskyt Mountains came together and built a fort at the mouth of the valley, near the Lifespring Chasm. What started as little more than an outpost now stands as one of the preeminent examples of dwarven construction and houses the largest and longest running joint military operation in the known world.
Indeed the Fort proper is technically only the northern-most in a series of 12 forts that spans the 73 mile gap that is the entrance to the Emerald Hills. That being said, since all the people patroling the walls wear the same crest, the whole wall has aquired that name. All the forts, should you come upon them, as well as the walls seem to have been pulled as a solid piece of stone from the ground. While possible for a group of sufficiently skilled dwarven casters this is not the case, instead the seams between the quaried stones were sealed by magic.
Upon the walls at and between these forts patrols pass with surprising regularity. The purpose of these patrols is two-fold. They burn back the encroaching moss upon the wall with extreme prejudice. While the walls may be granite the majority of their black color has much more to do with the soot from these patrols. The second purpose it to kill any birds or other creatures attempting to pass from the Emerals Hills back over the wall.

The Lifespring Chasm

Abutting the northern end of the Fort of Burning Elk and running all the way to the Myrskyt Mountains is a seemingly bottomless chasm from which running water can be heard. It is admittedly bigger than recorded on the oldest maps, a reminder of the series of severe earthquakes that struck the region in 4678. It is at least 1,000ft deep, but few enough expeditions have been mounted to explore it. It is an effective barrier against the spread of the moss, and probably the source of the river that emerges from the hills some 25 miles north.
There are several reasons the Chasm has not been too heavily explored. The main one being that water constantly flows down the walls. Where the water comes from, or indeed where it goes since the Chasm has not turned into a lake are largely a mystery. The water is highly alkaline in nature, enough so that it will degrade most regular climbing equipment at a noticibly accellerated rate.

The Moss

No one knows where the moss came from. Did a wizard make it? Is it related to the crystalization happening on the other side of the mountains in the Tuulikello Forest? It is most certainly magical, a fact confirmed by a large number of magical researchers and several druid circles. Of course, similar to the Tuulikello Forest the druids claim that it is a natural phenomena and have not taken any action against it that anyone has been able to determine.
It is... not quite carnivorous. Animals wander in, either goats or other cliff dwelling animals from the mountains or up from the foothills and the edges of the Viidakko. Then they sleep, and the moss rather rapidly covers the unfortunate creature... completely covers, outside and inside. There is no doubt the process kills the creature. Well, sort of?

by Drunkenpanda951 with Midjourney

I mean the creatures can move, but more naturally (usually) than one would expect from a zombie or other "puppetted" animals. Those at the Fort will tell you of deer, tapirs, even the occasional jaguar. Just, covered in moss instead of fur and with glowing green eyes. Also, while the "animals" in question usually move nautrally, sometimes strange things are observed. Like a jaguar bounding around like a goat, or a capybara moving with the halting gait of a sloth. Exactly a week later the animal crumbles, releasing a small cloud of glowing spores into the nighttime air with not even a skeleton left over. The moss spores settle onto the hills and rapidly blend into the rest of the landscape.

Where they can be seen?

Yes, you read that correctly. Strange as it may seem, a vast majority of the walls are one-way walls which are a speacialty of the Dwarf Clans in the Myrskyt Mountains. This is why it is incedibly important to ONLY APPROACH FROM WHERE THE FORTS ARE. Once you feel the slight shiver of passing through the one-way wall you are, most likely, doomed. The use of these walls was one of the few ways that was determined to allow "food" into the Hills but still keep it from escaping. Much easier than rounding up and mainaining livestock.