The Garden of Unearthly Decay

The Garden of Unearthly Decay is a swampy region that overlays itself on other areas. It warps itself to fit the place it settles, and is filled with life, albeit of distorted or warped versions of life. What causes it to appear is open to speculation. Rarely seen or encountered it appears randomly at different points in time & space, and even worlds. It appears to be some type of pocket dimension that travels the Material Plane settling on a part of other worlds.

Geography

The Garden is a mix of outright wetland & swamp. Marshy areas are bounded by clumps of sodden earth and dirty water holes. Plants are rife, all of them perfectly adapted to this environment. Small water courses and ponds are present running through parts of it, and some are that chocked with decaying matter and water borne plants they are easy to miss. Most of the waterways are surrounded by high banks, and some slopes here & there down to the water. The ground is harder in places with stones & small rocky outcrops, and the remains of either overgrown plants or buildings. Some parts are slimy, and the ground or water is covered or filled with a bubbling yellowy green slime. Trees have took root in places with a few of their roots exposed in places where the ground has worn away. Other parts have the roots holding it in place firmly. A minority of places has sand & sandy soils, with a few of them holding quicksand.
A low-lying cold mist sometimes forms over the Garden sometimes obscuring parts making it hazardous to travel. Other times, the Garden is almost tropical in temperature. In every case there is a darkness about it, with colours of brown, green, yellow, and cream being regularly seen. It somehow fits perfectly into wherever it appears, and to all intents appears to be a natural feature.
Only one thing that appears out of place here is at the centre is three damaged crumbling circular towers at the centre. These all have a design of three skulls carved into the old stonework, though can be hard to spot at a distance due to parts being covered in plant life. Most notice it is hard to reach these, and no matter how long they travel here these towers always appear just out of reach. It also seems that the Garden is larger than it looks, taking many longer to get to the edge of it than it is to get deep into it.

Ecosystem

The Garden is teaming with life of many kinds. Mosses & lichens, grasses, lilies, vines, reeds, sages, cattails, ferns, nettles, ash trees, and some pine trees & the odd small oaks are found throughout the Garden. Shrubs & bushes of all kinds can be found in small patches, usually along with the trees. Sometimes the trees are covered in vines, and both theses trees and shrubs / bushes are smaller than normal. In a few cases they are dead but to a degree appear alive with mosses & lichen growing on them. These latter organisms sometimes grow on rocks or the edges of pools of water.
There is plankton at times that bloom in the water which feed the plants when they dies. When living, they form the first step of the ecosystem, helping animals as a source of food. Annelids, insects, and arachnids thrive here, in different sizes, some longer and/or larger than a fully grown man. Most of the annelids are standard earthworms, churning up the soil allowing it to keep moist. A few are in the form of parasitical annelids, the worst is the different types being leeches found throughout the Garden. Tales abound of exceptionally long worms living in the waters feeding on detritus and any animal they can catch. Insects are common, with bluebottles, bot flies, and mosquitoes being the bulk of these. Some grow large, as big as a human adult fist, feeding on rotting organic material, or the blood of other creatures. Many spread diseases too, many of the most grotesque found on any world, and a minority that stinks of magic, very powerful magic. Spiders exist here too, both on land and in the water preying on others, and again, some seem to grow larger than usual. All types are present, as do a good number of scorpions and tics. Al the toxins present appear much more lethal than normal, and the tics seem to carry some of the most virulent diseases known. Also, waterborne diseases, and toxic plants grow easily with only the local animal life able to survive with them.
Fish are present in small numbers, usually trout, salmon, pike, and eels (which are the main fish present). Isopods are present to a small degree, usually living parasitically on the fish. Sometimes they seem to become aggressive enough to feed or parasitically infect other animals present. The eels can grow to a good few feet in length and are known to swarm other creatures that go into the water. Birds are extremely rare, with the exception of herons & magpies, who seem to thrive. Most other animals are pretty much non-existent, except for frogs, toads, snails, slugs, rats, and snakes. Like most other animals here, some can grow to exceptionally large sizes attacking any creature that wanders into this domain.
On rare occasions, other animals are found in small clusters. These are usually animals that have came from outside and have managed to survive by avoiding the worst here. They only seem to survive for a few generations before they are wiped out by the existing ecosystem. Also to note, is the amount of fungi & moulds that exist, growing anywhere & everywhere they can. Some can even be found living on animals. Many animals that survive are disease carriers or toxic in some way, besides the many inedible plants, making it difficult for more sapient species to survive for long.

Ecosystem Cycles

It follows local patterns when it appears and can stay long enough to witness any natural changes.

Localized Phenomena

The organisms are especially aggressive compared to others of their kind. The majority seems to carry toxins and/or diseases that are borderline deadly at best, and out-and-out lethal at worst. Most do not shy away from potential food sources, and will actively hunt any organism that travels into this domain.
What studies that have been carried out by sages & magicians within the boundaries of the Garden have recorded a number of strange phenomena as follows:

• If the three dilapidated towers are examined, there seems to be a powerful nexus point of unnatural dark magical energy from the point directly centre of them.
• Minimal animal remains are found, including skeletal remains. Either they are broken down by the local wild life, or are overgrown very quickly.
• The magic found at the towers seems to emanate across the Garden, blown about by gusts of wind. The same magic seems to saturate the whole Garden to some degree, fading away from the region when it disappears in a matter of days.
• When anyone feels the winds, they also can hear a mix of sounds if unlucky. These range from a dolorous bell sound, to voices chanting numbers, to chants to some thing 'beyond' (Grandfather Nurgle, Papa Disease, Lord of Decay, the Ninefold Decay), and the sounds of millions of flies buzzing.
• Any object or piece of equipment that has spent any length of time in the Garden starts to breakdown, rust, or decay at an exceptionally quick pace. Only by removing it does this stop.
• Strange footprints are sometimes seen in the grasses & the mud or sand. Many are strangely shaped, from misshapen humanoid feet, to massive elephantine shapes dragging a weight between them, to miniature versions, as well as slimy trails similar to those of slugs stretching a few feet across.
• Nothing is left of the Garden remains when it disappears, except the odd disease or victim of toxins. Nothing that dies there remains behind either. Also, the Garden randomly disappears but usually remain at least 9 days or 9 months at a location. If it vanishes with any creature still in it, they disappear too.
• There is a constant strong smell of decay present, and gets stronger when the wind blows. Also, the constant feeling of something unnaturally welcoming at the back of the mind, constant dreams of jovial gurgling laughter, and the feeling of being offered a bargain. The bargain seems to want the creature to offer itself up to a being of immense size in return for an immortal life free of of disease, pain, and hardship.
• The odd glimpse of warped creatures just outside of one's vision, of cyclopean beings with distended guts, some split open and one twisted horn on their heads carrying rusted warped weapons, in pox marked hands, attached to diseased greenish skinned bodies.
• Another rarer glimpse is a being shrouded on a half skeletal horse, watching the person from afar.

That is the most common tales concerning this land.

Fauna & Flora

Mosses & lichens, grasses, lilies, vines, reeds, sages, cattails, ferns, nettles, ash trees, and some pine trees & the odd small oak, shrubs & bushes of all kinds can be found in small patches, usually along with the trees.
There is plankton, annelids, insects, and arachnids thrive here, in different sizes, some longer and/or larger than a fully grown man. Most of the annelids are standard earthworms, churning up the soil allowing it to keep moist. A few are in the form of parasitical annelids, the worst is the different types being leeches found throughout the Garden. Tales abound of exceptionally long worms living in the waters feeding on detritus and any animal they can catch. Insects are common, with bluebottles, bot flies, and mosquitoes being the bulk of these. Some grow large, as big as a human adult fist, feeding on rotting organic material, or the blood of other creatures. Many spread diseases too, many of the most grotesque found on any world, and a minority that stinks of magic, very powerful magic. Spiders exist here too, both on land and in the water preying on others, and again, some seem to grow larger than usual. All types are present, as do a good number of scorpions and tics. Al the toxins present appear much more lethal than normal, and the tics seem to carry some of the most virulent diseases known. Also, waterborne diseases, and toxic plants grow easily with only the local animal life able to survive with them.
Fish are present in small numbers, usually trout, salmon, pike, and eels (which are the main fish present). Isopods are present to a small degree, usually living parasitically on the fish. Sometimes they seem to become aggressive enough to feed or parasitically infect other animals present. The eels can grow to a good few feet in length and are known to swarm other creatures that go into the water. Birds are extremely rare, with the exception of herons & magpies, who seem to thrive. Most other animals are pretty much non-existent, except for frogs, toads, snails, slugs, rats, and snakes. Like most other animals here, some can grow to exceptionally large sizes attacking any creature that wanders into this domain.
On rare occasions, other animals are found in small clusters. These are usually animals that have came from outside and have managed to survive by avoiding the worst here. They only seem to survive for a few generations before they are wiped out by the existing ecosystem. Also to note, is the amount of fungi & moulds that exist, growing anywhere & everywhere they can. Some can even be found living on animals. Many animals that survive are disease carriers or toxic in some way, besides the many inedible plants, making it difficult for more sapient species to survive for long.
There are stories that some of the lotus lily seed pods found in the Garden can fire their seeds at range at creatures causing damage. Another is that the seed pods also have maggot-like worms growing in place of seeds that eventually turn to bot fly like creatures that infect other creatures. They follow the same pattern as the seed pods, growing in the flesh of other creatures, eventually killing the host which is them used as nutrients for another lotus lily. 
There is another tale that crocodilian creatures have been sighted in the waterways waiting to pounce on the unwary. Not much evidence has been proven so far with this.

Natural Resources

Many toxins and diseases are present in the ecosystem, and are prized for their lethality. Many hunters will enter when this is discovered. Unfortunately few return.

History

The Garden of Unearthly Decay has been a legend on some worlds since time immemorial. It is linked to ill omens where it is believed that all natural & unnatural diseases & toxins come from, and that it quickly looks to kill & break down all life in the Material Plane. Linked to some ancient god that was birthed at the start of the universe, it embodies the idea of entropy & death, and the eventual breakdown of the Material Plane.
Yet at the same time, it embodies the notion of rebirth, and the most aggressive of lifeforms to survive no matter the odds. Every time it touches a world, a few are left with a new appreciation of life, and fewer still with a new deity to follow. None speak of it though. In some cases both healing spells and those linked to disease, decay, rot, & poison is bolstered or learned anew by others. 
In every case there is little to go on, but is linked to a pantheon who exists only to corrupt the mortal realms with their power. This is along with stories concerning four great powers vying for permanent access to the Material Plane, and the need for worship.

Type

Wetland / Swamp