Much of the surface if Overworld is covered in various types of forests. Varying widely from region to region, most forests share a common theme of being incredibly hazardous to outsiders and those without ranging and combat skills.
The most common types of forests in Overword are rainforests, both tropical and temperate. These dense wooded areas can extend for hundreds or even thousands of miles, and many areas are completely unexplored. Legends tell of any number of dangerous creatures, hostile jungle tribes, hidden ruins, and secret artifacts hiding in the rainforests of Overworld, and most of these legends have more than a grain of truth in them
Bullywugs, kuo-toa, and lizardfolk are extremely common in forested areas, and many areas will see all three fighting for control of a particularly rich hunting ground or strategically important ancient ruin.
Some rainforests are so ancient that their tallest trees rival the skyscrapers of large cities, and any one of these trees can hold multiple tribes of warring or peaceful creatures. A few rainforests on flat plains seem to have mountains because some of their trees are so tall.
Most temperate forests exist on mountains, or in transition zones from plain to mountains. These are common places to find bandits, outlaw towns, and to run across people who probably don't want to be found. Many temperate forests have been cut down over the past few hundred years as industry has picked up, though many are starting to grow back now that most construction is done with metal and stone.