I'm currently in front of the Swamp vault, unfortunately for me it's the undead vault ending, and i don't have anything that can provide me more than 1 level of negative resistance and even so it would mean getting rid of an item that give me good bonus, so if i go inside with all those clouds i'm going to be drained a lot and certainly die anyways.
As my character has a nice 13 skill in Earth and 15 in spellcasting, and a geomancy book i remembered there was a spell to break rocks and stones, i went back to my stash and learned Lee Rapid Deconstruction, so i could use it to make an entry close to where i think the rune is, avoiding a certain death in those vault clouds.
I looked up the lrd spell need "60 power" to destroy a stone wall and "80 power" for metal walls.
Fortunately, the vault use actually stone wall, so it looks like i will not need the higher spell power
My power level for LRD looks rather high, so i imagine it's more than 60 :
But using it multiple time on 1 single stone wall of this vault result in "the wall shatters" , it makes an explosion (and kills things behind that wall as i get experience) , but the wall is always there, and i must have used lrd at least 20 times on that stone wall.
What kind of game mechanics am i missing that prevent LRD to destroy those damned stone walls ?
EDIT :
the game mechanics i was missing is randomness, in fact the walls are destroyed randomly, i threw 20 LRD on a wall that shattered 20 times but stayed there, then LRD another wall in another sector and it exploded and disappeared in the 1st cast.
Tried that on several walls, some took 15 hits before disappearing too.
So yes, it's apparently random.
EDIT 2 : got the Swamp rune !
It was indeed located where i thought and after dozen and dozen of LRD finally a wall near the rune disappeared, allowing me to fetch it with very few contamination from the pestilence clouds (though it was only few turns but i got rotted 2 times , poisoned and slowed down, good i have lot of healing potion to counter the rot).
Without LRD due to the lack of negative resistance items i have, i would never have been able to get that rune.