The Underground Passage is located in the Stony Field area of Diablo 2 Resurrected. To find the Underground Passage, you must progress through the game and reach the Cold Plains. In the Cold plains, there will be a path that splits off into the Stoney Field.
Once you reach the Stoney Field, we recommend turning the automap on through either the options or the middle mouse button or tab. After this, you will need to explore the entire area as the placement of the Underground Passage varies and is random.
Related: How to switch to Legacy mode in Diablo 2 Resurrected?
It will look like a cave icon when you find it, as shown below. Inside you will find the way to the Dark Forest, which is a crucial step in completing one first major quest in Diablo 2. You will need to head inside the cave and progress all the way in until you find an area exit that leads out into the Dark Forest.
From there on, you will need to locate a tree somewhere on the map in the Dark Forest. You will need to find this tree and interact with it to retrieve a scroll. Find the scroll and take it back to Akara at the rouge camp. Doing so will progress the quest to the next crucial step to completing the Search for Cain quest.
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Andrew Vaughan is a Contributing Writer at Pro Game Guides that has written guides on popular RPGs and FPS survival titles for several years. Andrew Vaughan specializes in survival and roleplaying games and has been a lifelong gamer.