I uh... I did something amazing and horrible, of all the things I've done that might qualify as a war crime, this is the one I would get hung for.
I remembered Rumrusher being frustrated that you can't build in hell, the game doesn't "see" lumber down there on the slade floor, and I've been playing worlds without a hell layer for a while. This world is my second with a hell layer and the one where I really got the hang of building inside/through volcano tubes with collapses and punching holes into caverns for access and such.
Then I crashed when my macro bumped me past a lava flow into open magma while dropping water so I figured I'd go poke around in the nearby dark fortress and see if there was anything interesting I could do.
Once I got down into hell I stepped just outside and tried to build, expecting to get the "you can not build here" message, but then the screen popped up.
I had no lumber and couldn't use it anyways, so I figured I'd try to deconstruct the walls beside me, which much to my amusement worked just fine.
...then I noticed I had all of the dark fortress visible in my campstruction memory.
"Oh, dang, I guess it didn't wo-"
...
I did it.
I killed a dark fortress. I killed the people inside. I killed the beak dogs. I opened up a direct route to hell. I didn't do it with axe or fist, I didn't do it one by one, I did it with engineering, and it is permanent.
I can't build anything there, I can't seal the hole, all I can do is walk away and ask myself a question: would it be right to leave the other fortress in this world intact?
...I think we all know the answer there.