The Oldwalls don't change very much. They're over a hundred feet tall on the outside and sixty wide and made of dark stone no one's ever seen naturally-occurring, the same dark grey across the entire continent of Terratus, and they've been there long enough for the land to sink them into water and for mountains to push them upward and mostly not to break under the strain. Some have rivers running through them and some have bridges and ramps over them but they're part of the landscape, more immutable than the land, and have been for long enough that when current civilization began 1300 years ago they believed them eternal and unchanging.

The are full of towering corridors and stairs and ramps and shafts, all mostly twenty feet wide themselves, and respond only to their own relics. The doors that open in the sides of the walls are almost always fifty feet wide and thirty tall and on stone casters which have never worn down and take Edict storms to push off their course.

And they contain Bane. Bane are ghostly, glowing masses of claws and teeth and anger, they cut through armor like it was air, they seem to exist to devour magic and anyone who uses it, and any mile of Oldwall will contain hundreds of them bound in little octagonal holes in the wall and summoned into the corridor, if intruders without whatever security passes the architects of the Elder Realms intended to give to people they wanted to allow inside, which is to say if anyone at all, passes nearby.

And sometimes there's Bane too big for one of those. There's a trap for one, here. Actually, three. One of them is a bubble twenty feet across with a Bane about twelve feet across trapped in it; two are empty, and shouldn't be possible to trip. And there's no one here to trip them.

But there's been an Edict recently, and the shape of magic is a little twisted, so a breeze of rusting dust comes down the hallway, and it triggers the summoning, and there's nothing to summon but it does anyway, and somewhere far enough away the builder never expected it, in a direction they didn't think to shield from, it finds something to grab that is being thrown in... sort of this direction.