The Forest
Forests are¸ traditionally speaking¸ a different world spilling into our own. Not only do the forests house animals and plants unseen and unknown to the modern world¸ but they are often a barrier between worlds; there are forests in the world that¸ once entered¸ do not exit back into our world. Some forests don't have an exit to speak of.
But as civilization has grown¸ forests are destroyed in favor of progress. In a particular forest in Germany¸ unnamed and forgotten by many¸ the forest is a mystery; it has established a reputation for evil.
The investigators have unwillingly entered this unnamed forest and must uncover its secrets if they want to escape.
This is a modern-day scenario for the Call of Cthulhu roleplaying game. It takes place in Germany in the summer of 2020¸ though any modern time period and the setting of Poland and Austria are also possible settings that can be changed with little prepwork.