The first Act of Baldur's Gate 3 takes place around the crash site of the Nautiloid and the Druid Grove in a setting that's as green and vibrant as it is rife with conflict. Players might already be overwhelmed by the sheer scope of the game by the time they hit 10 hours in Baldur's Gate 3 and realize they're not even halfway through Act 1.
The surface of BG3's Act 1 is enormous and dense, but lurking just beneath its surface is an even more hostile, even more lush and colorful, lattice of caverns. Called The Underdark, it's a place that many of the game's races call home, and others call a death trap. There are only a few Underdark entrances players can find, none of which are particularly easy to access.
Updated September 5th, 2023: Players will eventually need to make their way to the Underdark in BG3 if they play on seeing and doing everything the game has to offer. There are many ways to get to the Underdark in Baldur's Gate 3, with some methods much trickier and inconspicuous than others. Players looking for all the possible Underdark entrances in BG3 can use the following guide, which now includes a video.
Underdark Map & Underdark Entrances
As of the full release of Baldur's Gate 3, there are a total of four entrances to the Underdark that players can find, during the first act specifically. The Zhentarim Hideout elevator, the Defiled Temple puzzle in the Goblin Camp, the pit behind the Phase Spider Matriarch, and Auntie Ethel's mushroom circle all lead to vastly different parts of the Underdark.
The location where each Underdark entrance leads is highlighted on the above Underdark map. The red circles correspond with the entrances below from top to bottom – with Zhentarim Hideout at the northernmost circle, and the Mushroom Circle found at the bottom highlighted area.
- The Zhentarim Hideout elevator leads to an area northeast of the Myconid Colony.
- The Phase Spider Matriarch leads to an area overlooking the Underdark near Minotaurs.
- The Defiled Temple puzzle leads to the magically guarded Selunite Outpost.
- Auntie Ethel's Mushroom Circle leads to a platform above the Arcane Tower.
A fifth entrance to the Underdark is technically also available through the Grymforge. Once players have already entered the Underdark and made their way to the Grymforge, they will unlock a Waypoint near the Gwymforge docks. By traveling to this Waypoint and taking the boat back to the Underdark Beach, players can use this fifth Underdark entrance. It's also possible, of course, to enter the Underdark via any Waypoint discovered down there just by traveling to it – open up the map and select one of the unlocked Underdark fast travel locations from the right-side menu.
Method One: Elevator at the Zhentarim Hideout
The Zhentarim Hideout is found to the north of the Waukeen's Rest Waypoint, which itself is found in the furthest northwestern area of the Act 1 map. After saving the trapped victims of a burning building, players can walk into a shack just down the street to the west where they will be surprised by a Sorcerer.
If players don't kill the Sorcerer and can use Ability Checks to make their way through without causing alarm, they can get through to the hideout with relative ease, after convincing a few more characters. Behind an illusory wall, in the northeast of the hideout, players' passive Perception can reveal a hidden room. A Secret Elevator to the Underdark is found in this room, but to use it, players must either unlock it with Lockpicking or pickpocket a Mechanical Key off a nearby guard.
Be sure to quicksave and use your stealthiest companion to not alert the nearby outlaws, if you didn't kill them all.
Method Two: Feather Fall In Phase Spider Cave
One of the Underdark entrances that players can find is located past – and beneath – a Phase Spider Matriarch. The ability 
Feather Fall negates fall damage from jumping too high, and there's a pit in the Whispering Depths that players can jump down to reach The Underdark.
The Whispering Depths is the home of a Phase Spider Matriarch and other arachnid enemies. It's a boss that's nearly impossible to avoid, and it has a lot of health (and allies). Kill the smaller enemies first, then go for the Matriarch when she's the only threat. At the end of the tunnel, there's a pit that the Matriarch was patrolling around.
At the pit in the Whispering Depths players should give every party member Feather Fall, then enable Turn-Based Mode. Make each character jump into the pit to gently fall down this Underdark entrance.
Method Three: Selune's Puzzle in the Defiled Temple
In the Defiled Temple, an area that can be accessed through a doorway in the western Shattered Sanctum, the Goblin Camp's HQ where players kill (or befriend) three True Souls to save the Druid Grove. Lockpick the doorway to transition to the Defiled Temple, where an Ogress roams. Either kill the Ogress or pass a Dialogue Check to proceed.
Follow the hallways to find a room with four rotatable circles on the ground, each with some filled and empty slots. Players must rotate these interlocking platforms so that the four empty slots are all on the bottom circle, where the light shines in from above. Once complete, flip the lever at the other end of the room, and progress downwards into the Underdark, specifically the Selunite Outpost.
Method Four: Whispering Masks, A Hag, And A Mushroom Circle
The fourth and final – and arguably most dangerous – way to find an Underdark entrance is through a Mushroom Circle beneath Auntie Ethel's Teahouse in the southeast of the Act 1 zone. Here, players learn that Auntie Ethel is indeed a hag, and can interact with her fireplace to discover a hidden lair that goes deep underground.
Before taking this route to the Underdark, pick up a 
Whispering Mask on a table in the cauldron room. The table is right next to the tree-like face that blocks passage to the room full of Cultists. Don't put it on until the party has defeated Auntie Ethel, though, which is doable around level 4 to 5. Otherwise, putting on the mask will render the wearer under the Hag's control (without other protective effects like 
Protection from Evil and Good, that is).
Once defeated, find your way around the lair (without triggering traps, if every party member has a mask equipped) and look for another tree-like face. Wearing the mask reveals that this too is a secret entrance, one that hides a mushroom circle leading to a platform just above the Arcane Tower in the Underdark, with another Mushroom circle that leads down.
Baldur's Gate 3 is available for PC, and is set to release on PlayStation 5 on September 6, 2023.