Upon arriving at Grymforge, you later find that True Soul Nere has been trapped along with some Deep Gnomes behind a cave-in.
If you need to rescue Nere and/or the Deep Gnomes, finding a way to blow up the cave-in will be necessary and there are multiple sources for explosives.
One of the sources is from a Deep Gnome named Philomeen and she has fled somewhere within Grymforge.
Philomeen Location
Philomeen has fled to a hiding place that only the Deep Gnomes know about, which is where they intend to meet up if something goes wrong.
The rest of the Deep Gnomes have been enslaved but Philomeen had escaped after setting off an explosion and may now be found in the northeast part of Grymforge.
How To Find Philomeen?
You may first discover the quest called Find the Explosives after heading to speak to Sergeant Thrinn, which requires you to find a way to blow up the cave-in.
If you speak to some of the Deep Gnomes, you can listen closely with an Ability Check and learn about Philomeen and persuade them to tell you more.
This begins the search for explosives that Philomeen is said to have with her and will take you to a certain section of Grymforge.
To make your way to Philomeen, you will need to head back to the area where you docked and go to the two Duergar who are tossing Deep Gnome bodies into the water.
There is a large gate near the two Duergar and you must decide to either convince them to leave or to kill them before you unlock the gate and make your way inside the dining hall.
If you look around the hall, you will find that there is a button on a closed portion of the wall, and pressing it will open a path.
Continue making your way by following the path and progressing to the very end where there will be a large gap that you and your party will jump across.
You will find a large, abandoned building with a locked Intricate door but this does not need to be lockpicked since there is a large, destroyed section of a wall on the other side.
Go around the building and you will be able to enter, revealing that Philomeen has made it to the hideout where they were supposed to meet.
Getting Explosives from Philomeen
Once you go near Philomeen, a cutscene will begin and she will warn you about the Runepowder that is about to explode if you try to take it from her.
This will eventually end up with her blowing herself and your party up if you don’t agree with her or if she is not convinced. (She will only offer you the Vial and not the whole barrel of Runepowder)
You will need to pass the Ability Checks to convince her to stop being hostile and once you have talked her down, she will offer you a vial of the Runepowder that she has with her.
It is optional to kill Philomeen to take all the powder, but you can settle for the vial instead as it is more than strong enough to destroy the cave-in.
Verdict
Finding Philomeen is not that hard since you just need to follow the path after going through the dining hall that leads to her hideout.
Along the way to the dining hall, there is a metal door that can be opened, and you may find Smokepowder Satchels inside, allowing you to conserve what you get from Philomeen.
If you plan on using the Runepowder Vial to destroy the cave-in, tossing it will make the others move out of the way and you can ignite it afterward.