The Underground Passage
This tunnel is basically just what the name says, an underground passage. It extends from the outskirts of Trauma. To the sun-covered cliffs of Sonalit.
In order to enter this passage, you need to have the The Deepest Roots quest completed. This passage is full of monsters such as the Slime, Bat, Bandit, and Wolf. There is an easy way for higher level players to travel through here, and even a new town to be discovered by high-leveled players. To newer players, the Underground Passage is a great place to level their hirelings, so feel free to try it out.
There is a quest chest in this passage that carries some nice items to those newer players.