Swamps are the archetypical wetlands: they combine the treacherous pools of mires and the labyrinthine waters of marshes with the dark cover of trees. Water moves slowly, and the trees are adapted to these locations: many of them grow long roots that resemble the legs of spiders, which form perfect hiding places for amphibian creatures. The trees offer shade, but also a way to move for some creatures.
For humanoids these locations are difficult to traverse, maps of large swamps are rare, and orienting oneself using landmarks can be impossible because of low visibility. Even a short distance can take two or even three times more travelling if there isn’t an experienced guide to help the adventurers.
While bogs and marshes have their uses, swamps are commonly regarded with fear. People tell horror stories about the things hidden in the swamps in hushed voices around the warmth of a hearth. Many of these tales are overexaggerated, but there’s no telling what horrors lurk hidden in these places: kobolds, hags, lizardfolk, even black dragons build their lairs in swamps, which is enough to keep any sane person out of these areas.
However, swamps are also abundant with precious rare resources and hidden treasures. The waters are abundant with life unique to these locations, such as birds, amphibian creatures and many rare plants. Swamps are also perfect places to hide bases of operation, cult temples and secret laboratories. After all, no-one in their right mind goes to a swamp without a good reason.
At times a swamp may be located near the ocean, creating a saltwater swamp. These locations host a completely different fauna compared to the freshwater swamps that are mostly found inland near rivers: crabs and other sea creatures come to these locations to spawn in the quiet waters. The creatures that live here can survive in brackish water, but humanoids travelling in these locations may find themselves confronted with the sailor’s dilemma: being surrounded by water too salty to quench their thirst.
Saltwater swamps can be difficult to move through depending on the weather and the tide. The water levels can change dramatically, depending on the conditions. Because of this, there may be locations hidden by the high water that are only exposed when the water levels are low. Exploring these locations has a time limit, though: when the waters rise, these places can flood quickly and become death traps to those too slow to realize what is happening.
But consider special encounters. Because cults often hide in swamps, there is almost an overabundance of strange altars. Many cults are short lived, but while the cult may be long forgotten, the altar remains as a powerful reminder of the cult’s sinister glory days.
Many of these altars are still capable of terrifying magic, if would be worshippers provide a sacrifice. Some of these altar magical effects may be deadly or overpowered, so discretion is advised.