To enter the Baldur's Gate 3 underground cave, you can use Mage Hand or Small Animal Gasification. Usually, these small holes are entered in this way, and the task can be completed after entering.
Answer: The main thing is to use the hand of the mage or the gasification of small animals.
The first is to go all the way down from the Goblin Temple of Sullun, and you can enter the Dark Territory.
You can still enter the Underdark by using the Featherfall spell from the Spider Queen's cave to jump down into the pit.
Players can also enter the poisonous gas area of the tree in the hag house fireplace and go through the hidden door in the tree.
Then you have to pass through the two staffs and then you can smoothly enter the dark area.