One important area you must enter in Act 3 of is Bhaal's Temple, where Orin the Red holds an important Netherstone. However, it is far from easy to reach this location as you fight through hordes of cultists that reside in the bowels of the Lower City. You also need a special item to open the path forward into the lair of the god of murder.
There are minor spoilers for main story quests in Act 3 from this point forward.
While you try to find ways to gain one of the Netherstones from Orin the Red, she might take a companion hostage and threaten to kill them. Your roleplay choices affect Orin in by influencing which character gets kidnapped into Bhaal's Temple. Your pursuit of important artifacts transforms not only into a quest for a crucial quest item but also a rescue mission against time to save your ally.
You can find the entrance to an underground path leading to Bhaal's Temple north of the sewer system within the Lower City of . There are many ways to enter the sewers throughout the City, but the best way is through the two entrances located in The Guild. This place, run by NPC Nine-Fingers Keene, can be visited toward the west of town as your party continues to explore Baldur's Gate.
The door you find will be locked shut, showing a diamond-shaped cavity in its center, while a hanging body bleeds onto a circular stone right in front of it. Near this door is a fast-travel Waypoint you and your party can use to leave and come back once you find out how to proceed forward. Feel free to shoot down the hanging body so that its blood collects on the circle below it to open the door into Manslaughter Chasm.
Many enemies occupy the Chasm, including a powerful group of Bhaal cultists led by Farslayer of Bhaal Ghislev. You need to defeat this zealot before he can cast Power Word Kill and instantly kill every member of your party in. Far enough into the Chasm, you'll find another set of doors like the ones leading into this area, but this obstacle can only be unlocked
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