You'll need to find where the Diablo 2 Underground Passage is, fairly early in. The location pops up when you're looking for the Dark Wood and Tree of Inifus to recover a scroll. The problem is that you're given no information on where to look, or even what you're looking for. Aaand the maps are randomly generated so the underground passage will be in a slightly different place for everyone.
However, there are some things that will help you find the Diablo 2 Underground Passage by narrowing down the area you need to search. So let's take a look and get you to the Dark Wood. And, if you're not sure about your choices so far check, out our guide to the best Diablo 2 classes if you're thinking about a reroll.
How to find where the Diablo 2 Underground Passage is
Here's how to identify Diablo 2 items if you were wondering what loot you've actually found.
The search for the Diablo 2 Underground Passage appears as part of the third main quest, The Search for Cain. Now, as we mentioned, Diablo 2 maps are randomised, making where the Underground Passage actually is impossible to pinpoint precisely for everyone. However, there's a few things you can do to help you find it faster.
For starters the Underground Passage is in Stoney Field, so head there to get started. Hopefully at this point you've found the waypoint and can just fast travel there from the Rogue Camp. If not, keep an eye out for the grey stone square of the waypoint while you're there.
The second thing that will help you is that the Underground Passage entrance is always on the edge of the Stoney Field area. So find an outer wall and hug it all the way around until you see an entrance on the mini map. If you see any roads heading outwards, that can give you a clue as well. Basically you're looking for something like this on the mini map:
When you see a door like that, head to it and enter to get inside. However, you might want to explore and grind a bit before you do as there's a fairly decent amount of resistance inside for lower level characters, from things like Vile Hunters and Misshapen Tainted. They can quickly end your adventure if you're pushing your character's level too soon. Definitely talk to Kashya in the Rogue Camp too about hiring a mercenary to come with you as well, if you haven't already.
Once inside the Underground Passage you'll be able to progress to the Dark Wood on the top level, or head lower to explore and grind first.