A criminal group's underground base called The Zhentarim Basement is one of many hidden locations you can find and enter in Baldur's Gate 3 by interacting with the right people. A place filled with items, side quests, and other points of interest, this hideout provides even more content to this massive RPG. Hidden inside this place could also lead your party to the infamous Underdark for the events of Act 2.
Before you even start trying to find the Basement, go ahead and either teach a character in your party the 
Detect Thoughts spell or find a scroll with this piece of magic ready for use. Those hiding from the law likely need to find out how to get into their base, making this magic important for breaching their defenses. Though not the greatest secret in Act 1 of Baldur's Gate 3, the Zhentarim still have plenty of ways to repel your group.
How To Find The Zhentarim Basement
To find the Zhentarim Basement, travel to the Waukeen's Rest Waypoint, northwest of the Blighted Village that hosts several burning buildings from recent goblin attacks. Head further northwest past the central fountain of this small village until you spot a dead ox on the ground. Go right where you might see a door blocked by boxes, and remove these obstacles to enter this Small House in Baldur's Gate 3.
As soon as you enter this place, a guard named Salazon will be hostile toward your group after a short cutscene that places you into some tense dialogue. In the "Find the Missing Shipment" quest in Baldur's Gate 3, where you may have saved the NPC Rugan from gnolls along the beach, he will have told you about the for the group Salazon guards. You may also use Detect Thoughts or other powerful spells in Baldur's Gate 3 to figure out the code.
Repeating the code to Salazon will prevent you from having to any Charisma-based checks, as the guard will instantly assume that your group is part of the underground organization. Salazon will tell you that the path to the Basement is downstairs past the nearby Hatch. Travel below and unlock the wardrobe using the key Salazon gives you to reach the Zhentarim base, where you'll meet someone new.
How To Enter the Zhentarim Basement
Past the wardrobe, you will find another fast travel spot and the Iron Gate leading directly into the Basement itself. Before you can enter, though, the leader of the gang here, Zarys, will stop you in your tracks, demanding to know why you have come here. Threatening the lives of you and your party in Baldur's Gate 3 for tresing, it will take more than the code you gave Salazon to make it into the criminal base alive.
All you need to do here is a Persuasion, Intimidation, or other type of check to convince Zarys that you mean no harm. Doing this may lead to Zarys giving your group a job or just letting you in with a threat not to mess with her gang. When you find and enter the Zhentarim Basement in Baldur's Gate 3, you can find a hidden age to the Underdark, pursue several quests, and buy a few powerful items.
