There is a quest in Grimforge to get powerful explosives.
To get the whole barrel, and not just a small piece, you need to do a very non-obvious action:
Take a player with a strong ranged attack (bow or crossbow). Carefully guide him in such a way that he can hit Philomeen without triggering a cast-scene.
Next, it takes a bit of luck to kill her on the first try.
Congratulations, you have a 10d8+36 force damage bomb with a huge radius and cost 2500 gold
