Location: Black Forest

Another post for the "23 Unbelievable Places" series, with credit to Reddit user Boatakk. This is a case where I couldn't really think of too much to say about the setting, but I really liked the ideas that I had. 


Description:
The forest is dark and surreal. The trees are bent and irregular, and are crusted with black, twisted bark. A faint blue fog permeates the entire forest, and seemingly clings to your body as you move. Putrid yellow flowers grow in random spots, their petals apparently covered in a sickly ichor. The air is cold and moist, and the grass is spongy beneath your feet. This place is almost a swamp, and you can smell death in the air.

Associated Knowledges:
Nature:

• The plants in this place don't seem entirely natural.
• The flowers are poisonous, and seem to be choking out the life from the rest of the forest.
• The flowers are actually some sort of undead plant, and the trees are the withered husks that remain after being preyed upon. 

Arcana:

• Magic permeates the forest.
• The same sort of magic seems to emanate from the flowers.
• The magic is a mixture of natural and arcane, and radiates evil.

DM Info:
  The Black Forest is a den of evil. The exact kind of evil can vary depending on your needs - my basic ideas were a clan of satyrs, an evil necromancer, or a witch of some sort. In either case, the forest is highly unnatural. Spooky yellow flowers grow all around the place, but are actually a special type of undead plant. They have basically eaten all the life out of the other plants around here and turned them into more undead plants. The flowers themselves are poisonous. The way I'm imagining this is that the flowers are an experiment by whoever has made this forest their domain: a blend of natural magic and necromancy. All of the plants are, to some extent, the minions of the forest's master. He can either see directly through them, control them, or at least have a general sense of what is going on at all times within the forest. The flowers are especially connected to the master of the forest, and perhaps are sentient themselves. 
  Encounters in the forest should involve heavy usage of the flowers. They have a few special powers, such as being able to emit a cloud of poison, or sapping energy when they're touched. Since they're experimental in nature - pun intended - they should have different powers in different areas of the forest. The trees, then, should also have different characteristics depending on which flowers "killed" them. Examples I can think of:

• The "standard" flowers simply drain life out of anything they touch. The trees around them are wooden carcasses, and emanate negative energy.
• Another group of flowers actively puts out poison gas. The trees in that area have poisonous bark, and look more sickly than others.
• A different type of flower moves very slightly, with small tendrils grabbing insects in addition to killing the surrounding trees. It's victims are also reanimated, and the tree branches sway slightly, trying to push prey into the flowers. 

  Keep in mind that before this evil force arrived, the forest was still very much forestlike. Other groups of creatures such as fae, elves, or treants have been either driven off or killed since then. The ghosts or reanimated bodies of these creatures or plants could still be present in the forest. Perhaps even with infighting - the ghosts of those slain creatures are trying to reclaim or destroy their now corrupted bodies. Alternatively, their spirits are bound by the same evil masters of the forest for further experimentation. There's a lot of room for different weird and evil stuff to be happening with all of this. 
  The forest itself is larger than The Black Forest, which refers only to this place of evil. In the larger, more normal forest, the climate is more what you would expect in a forest, and all seems relatively normal. The closer the players get to this part, the colder and damper it gets, and the blue mist forms. The yellow flowers can not survive without that sort of climate, so it is magically maintained. However, the masters of The Black Forest are slowly trying to expand their territory, for further experimentation. Also because they're evil.
  The lair itself will just be a small grove in the center of the area. It will be surrounded by the standard sort of yellow flowers, as they are the most well-developed and were created first. It should be pretty small, I was thinking either a cave or an open grove of trees. Since the masters are likely spellcasters, they should have minions to protect them. 

Adventure Hooks:

• Local fae have been driven from their home, and have asked the players to help them.
• A great evil has been detected from the forest. The players have been tasked with destroying it.
• Necromantic minions are venturing further than they should be. The players investigate and come to this part of the forest.