I didn’t expect to write more of these… but I guess that’s what makes them off-the-cuff. I envision both of these as likely Starfinder campaigns, but you could mold them to work however you like.

Armageddon Helix: While there are numerous theories about its creation, no one is sure what caused the Armageddon Helix, a 525-mile wide strip of alternate reality running in a spiral from pole to pole of the Earth. Within the Helix, technology became unpredictable, magic and psychic powers bloomed, monsters arose, aline ruins and mythic buildings burst up from the land itself, and destruction was wrought. Magic does not function outside the Helix, but many strange technologies do. However, those technologies require materials that only exist within the Helix.
Those within the Helix changed as well, becoming unable to survive outside of it, and becoming ill if the come within a few miles of its edge. Similarly, those from outside the Helix cannot live near or survive within the Helix. Of course, this makes travel much more difficult–going from Seattle to Boise is simple enough, as they are within the same Safeland strip, but the center of the country is within the Helix, and travel to the East coast requires travel up to the north pole, around the end of the Helix, and back down toward North America.
The exception to this are extremely rare Apocalypse Riders, 0.01% of the population who can move freely between the Safeland and the Apocalypse Helix. Apocalypse Riders are heavily recruited, to take emergency supplies and news into the Helix, to bring valuable HelixTech materials out, to hunt down criminal riders who operate on the borer where few can seek them out, and to explore ever-changing Helix Ruins in the hopes of understanding what brought about the Helix, and if it can be reversed or controlled. Between missions, Apocalypse Riders can live in relative comfort in the Safelands, going to restaurants, seeing movies, and sleeping in soft beds. But within the Helix, danger lurks around every corner.

Gjallarbrú Guard: There are many names for the river that separates the lands of the living from the lands of the dead. Regardless of its name, that river is crossed by an infinite number of massive bridges, each bridge a city wherein the work of the afterlife is carried out. One of these is Gjallarbrú, the Golden Hall.
Souls dwell here. Mostly those who expect to reach a Norse afterlife, but others two. Some know how they got here. Many don’t. A few don’t even believe they are dead.
In most cases, those souls eventually move on. Once they pay their obolgild, or finish their limbo-punishment, or clear up some paperwork. Some don’t ever go on to the afterlife. Others can’t. And a lot just need to work to earn the obolgild to do so… or steal it.
There are rules, too. Cosmic, immutable laws. And fiends and elder alien reality-warpers and astrally projected living necromancers and sleepwalking psychics and Miskatonic university professors keep stirring up trouble. And sometimes, a dead soul even gets killed.
You are one of the souls that can’t, or won’t, move on. And you are part of the city Guard. It’s your job to keep the peace. The Peace of the Already Dead.
Sometimes Guards come from Chinvat, the bridge-city upstream from Gjallarbrú, chasing escapees who floated down the Infinite River. Less often someone must go downriver to Hardos, the broken bridge city, for similar reasons. Rumors claim that Guards are sometimes sent more than one bridge away up or down the river, but if that’s true, you’ve never spoken to such people.

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