Chell McSubject_Profession_Here has been content lately. She passed a test chamber lately. She admired a finely crafted portal gun lately. She was comforted by a companion cube lately. She lost a companion cube to tragedy lately.
She is a fanatic worshiper of GlaDOS.
She likes the colours blue and orange, and companion cubes for their loyalty. When possible, she prefers to consume Black Forest cake.
I love this idea
.
Thereby completely invalidating the goal of having a fortress.
That's like saying that kobold thieves completely invalidate the goal of having traps. Of course you wouldn't give it to just anyone, same way the average goblin siege doesn't come with a dragon. They'd be a rare occurrence - you'd be blissfully managing your fortress, picking opals out of some subterranean exploratory tunnel wall, throwing goblin chunks into the refuse pile and fuming at your nobles, when all of a sudden...
A horrifying portal has opened in thin air!What's this, you think, beholding the beautifully rendered ASCII wall that is the portal seen from above. Then, through the portal, a legion of fell beings and wizards starts to pour into the beautiful countryside. As you hurriedly activate your military and pray your civilians will have the courtesy to get inside quickly, you realize that
this will be a battle to remember.
The idea to have mini-portals from outside the fort to its insides is awesome, too, as is the idea that it can be prematurely destroyed by killing the mage who materialized it. I can just picture a wizard gathering a band of bandits of various backgrounds and races and plotting a murderous rampage on the settlements in the area. Portals as quick shortcuts to their innards might be but one part of his repertoire.
Only the mightiest mages can open it, but first they have to reach it.
The goblins have learned of this portal.
It is RIGHT in the middle of the mightiest dwarven civization on the planet.
You have discovered HFS!
It is a long forgotten portal!
It is being opened!
Urist McMiner has died of deadly neurotoxin!
A vile force of androids has arrived!