After traveling from the Underdark to Grymforge, you will mostly be arriving at the area due to exploring or quests, you will find that a certain True Soul is trapped in a cave.
If you are planning on helping the True Soul named Nere to get out, you will have to find a way to open a path.
This requires that you blow up the rocks as soon as you can or else everyone who has been blocked off will end up dying due to gas exposure.
Where To Find Nere?
Depending on how you enter Grymforge, you will be able to find the cave-in that is trapping Nere, which can be found by heading south.
If you have the Boots of Speed, which is part of the Find The Missing Boots quest, you can easily make your way there.
Other methods of passing safely through Grymforge will require Ability Checks to make the Duergar and other locals within the area non-hostile.
How To Free Nere?
Since Nere is on the other side of a cave-in, you will need to remove the blockage so he can get out and this does not involve a pickaxe or attacking with normal weapons and spells.
You will need to create an explosion to free Nere, which can be done in multiple ways depending on what you can get your hands on.
If you have any explosives, barrels and such that can create an explosion but there are other ways to do this if you talk to the NPCs in the area.
Once you have something to blow up the rubble, place it near the Cave-in and the others will move out of the way so you can create the explosion.
What Happens When You Free Nere?
After freeing Nere, he will be furious with how long it takes and start taking it out on the Deep Gnomes and look to you to finish the job.
He sets his anger towards the Duergar as well, which will result in you fighting them with him on your side or fighting against him with the Duergar teaming up with him.
Your encounter with Nere will allow you to fight him if you side with the Dark Gnomes but if the results end with him surviving, may find him in Act II.
What Happens If You Don’t Save Nere?
Once you reach the cave-in where Nere is trapped, you can choose to save him or not and if you choose to let him die, all you need to do is take a couple of Long Rests.
After the first Long Rest, Nere will try to contact you via the parasite connection that you both have and upon doing another Long Rest, he can be found dead.
This results in the Free True Soul Nere quest being completed, where it is stated in your quest log that the cave-in was cleared without your help. (Resulting in Nere’s death)
Using a Long Rest to progress without helping Nere will also result in the Deep Gnomes and their captors being gone, which ends the Save The Grymforge Gnomes quest.
Verdict
Grymforge is a large place for you to explore and there are multiple things that you can find, making it necessary to try to be friendly towards the Duergar until the time is right.
You can use any kind of explosives if it creates a blast that will clear the rubble and may wait for the enemies to clear out before blowing it up.
Attempting to skip freeing Nere may result in you missing out but this is also a way to avoid a difficult battle. (It is best to prepare before this)