Look. Everyone tells you that travel through the underdark bg3 is the "hard way" to get to Moonrise Towers. They aren't exactly lying, but they aren't telling the whole truth either. If you take the Mountain Pass, you get sun-drenched views and a Githyanki crèche that wants to murder you. If you go down below? You get bioluminescent mushrooms, eldritch horrors, and a verticality that makes the camera system cry. It’s dark. It’s damp. Honestly, it’s probably the best part of Larian’s entire masterpiece.
Most players stumble into the depths by accident. Maybe you solved the stone circle puzzle in the Defiled Temple. Perhaps you jumped down a literal spider-infested hole in the Whispering Depths with Feather Fall active. Regardless of how you arrived, you're now standing in a subterranean ecosystem that doesn't care about your surface-dweller problems.
Finding your feet when the sun goes away
The first thing you realize about travel through the underdark bg3 is that lighting isn't just a vibe—it's a mechanic. If you’re playing a Human, Lae'zel, or Wyll, you’re basically blind without a torch or a Light cantrip. Shadowheart and Astarion have Darkvision, which makes them your unofficial scouts. Don't underestimate the Light spell. Casting it on your melee fighter's weapon ensures that when they get close to a target, that target is illuminated, removing the "Obscured" penalty that tanks your hit chance.
Navigation here is a nightmare. Seriously.
The map looks like a spilled bowl of spaghetti. You have multiple levels, hidden ledges, and those obnoxious orange mushrooms that explode if you breathe on them. The Selunite Outpost is your safest starting point. It has those massive statues that shoot lasers at anything that moves. Pro tip: don't just run out the front door. Those lasers will turn a Level 4 party into ash before you can say "is that a Minotaur?" You have to disable the power source—a glowing Moonstone held by the central statue—or just find a side exit through a broken window.
The Myconid Colony and the politics of fungi
Once you push past the initial shock of the environment, you'll likely hit the Ebonlake Grotto. This is where the Myconids live. They are giant, sentient mushrooms who talk to you via "rapport spores," which is basically telepathy with extra steps. Sovereign Spaw is the leader, and he’s got a bit of a chip on his shoulder regarding Duergar slavers.
Working with the Myconids is the smartest move for your travel through the underdark bg3 experience. Why? Glut.
Glut is a secondary Sovereign you can recruit as a temporary fifth party member. He’s slow. He’s ugly. But he can resurrect dead creatures. If you kill a Hook Horror or, better yet, one of the Minotaurs near the gate, Glut can bring it back as a fungal zombie. Having a 100-HP Minotaur on your side makes the early combat encounters trivial. Just be careful—Glut has his own agenda, and it usually involves a violent coup. You’ll eventually have to decide if you want to help him overthrow Spaw or stay loyal to the original colony. Staying with Spaw is generally the "good" path, but Glut’s combat utility is hard to pass up for a few hours.
Dealing with the real threats: Beholders and Bulettes
Let’s talk about the Bulette. This thing is the "Jaws" of the Underdark. It burrows underground and pops up when you least expect it, usually knocking your squishiest caster prone. It doesn't stay for a full fight, either. It’ll hit you for two rounds and then dive back into the dirt, only to reappear later when you’re already low on resources.
The best way to handle the Bulette? High ground.
If you see the ground shaking, get your team onto the elevated rock formations. The Bulette’s "Leap" attack is devastating on flat ground, but its AI struggles more with verticality. Also, Cold damage is your friend here. Slowing its movement gives you more time to burst it down before it retreats.
Then there’s the Spectator. If you head toward the area with the petrified Drow (near the Selunite Outpost's side exit), you’ll trigger this encounter. It’s a mini-Beholder that un-petrifies the Drow to use them as thralls. Don’t kill the Drow immediately! If you hit a petrified Drow, the Spectator's charm breaks, and they might actually help you fight the monster. Or they’ll turn on you immediately after. Drow are complicated like that.
The Arcane Tower and the lonely robot
To the southwest, you’ll find the Arcane Tower. This place is a masterclass in environmental storytelling and a huge part of travel through the underdark bg3 lore. It’s guarded by Arcane Turrets that will shred you. Use the "Sussur Flowers" found near the base of the massive Sussur tree to the north. These flowers project an anti-magic field. If you throw one near a turret, it shuts down. Simple.
Inside the tower, you’re looking for a lonely construct named Bernard.
Bernard is obsessed with poetry. If you read the various books scattered throughout the tower, you can "speak" to him using specific lines.
- "Or art thou friend, a foe and bright?" makes him peaceful.
- "How can I trust? How will I ever know?" prompts a hug (yes, really).
- "The silence stretches on, and on..." makes him give you a ring.
If you don't read the books, he’ll probably try to electrocute you. The basement of this tower also contains the "Staff of Arcane Blessing," which is arguably one of the best early-game items for a Cleric or Wizard. It turns the Bless spell into a massive buff that adds extra 1d4s to spell attack rolls.
Navigation to the Forge
Eventually, your travel through the underdark bg3 journey leads you to the lake. To progress to Act 2, you need to take a boat. This leads to Grymforge, an ancient Sharan temple occupied by Duergar.
Grymforge is a vertical maze. You’ll be jumping across moving platforms and dealing with deep rotas (big cows). This is also where you find the Adamantine Forge. This isn't just a quest marker; it's a gear factory. You can craft two pieces of Adamantine equipment—usually the Scale Mail and the Shield are the best picks because they prevent enemies from landing critical hits on you.
The boss of the forge, Grym, is a giant mechanical protector. He is immune to almost everything unless he’s standing in lava, which makes him "Superheated." When he’s glowing red, he’s vulnerable to Bludgeoning damage. If you have a Monk or someone with a Warhammer, they are the MVP here. Or, you can just lure him under the giant central forge hammer and pull the lever to smash him for massive damage. It takes a bit of positioning, but it's satisfying as hell.
Why the Underdark beats the Mountain Pass
Look, the Mountain Pass is great for Lae'zel’s story, but the Underdark is richer. You get the Sussur Bark for the "Finish the Masterwork Weapon" quest. You get the "Phalar Aluve," a sentient sword stuck in a stone that sings or shrieks to buff allies or debuff enemies. You get the entire Omellum subplot—a Mind Flayer who actually wants to help you.
It’s a denser experience.
It’s also significantly better for XP. By the time you finish the Underdark and the Grymforge, you can easily be Level 6 or even 7. This makes the transition into the Shadow-Cursed Lands much smoother. If you skip this area, you're leaving thousands of points of experience and some of the most unique gear in the game on the table.
Actionable Steps for your Underdark run
If you're about to head down, do these three things immediately:
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- Craft the Sussur Weapon: Find the Sussur Tree, grab the bark (watch out for the Hook Horrors), and take it back to the blacksmith's forge in the Blighted Village. A dagger or greatsword that silences enemies on hit is a game-changer against the mages in Act 2.
- Stock up on Bludgeoning weapons: You’ll meet a lot of constructs and heavy armor users. Your fancy rapiers and longswords won't do much against a mechanical guardian or a Duergar in plate.
- Get the 'Phalar Aluve': It’s located near the Selunite Outpost. Even if your character isn't a Bard, the "Sing" ability provides a 1d4 bonus to attack rolls and saving throws for everyone nearby. It stacks with Bless. It’s essentially a legal cheat code for combat accuracy.
- Complete the 'Find the Mushroom Picker' quest: Saving Baelen gets you some thanks, but finding the "Noblestalk" mushroom in that same explosive field is the real prize. It can restore Shadowheart’s memories or cure certain conditions. Or you can sell it for a fortune. Just don't let it blow up.
Don't rush it. The Underdark rewards the patient. Every dark corner usually has a skeleton with a diary or a hidden chest. Grab a torch, keep your eyes on the ceiling for falling rocks (or spiders), and enjoy the glow. It's the most "Dungeons & Dragons" this game ever feels.