Adventure hooks you'd love to use, but can't.

[Roxxy]

In my case, it's because I have precious little time for gaming in the next few months. What I want to do in my magitech/modernish Pathfinder setting is start out the adventure by letting the PCs go on vacation in a major city (the PCs are field agents for a high level government agency, I should mention). Suddenly, the city gets nuked, and in the wake of the chaos a gate gets opened up, allowing demons to move through. Now, going by what a 12th level or so PF character can generally survive, it isn't too bad to let them survive a nuke. These are people who can survive being thrown off mountains or chucked into a volcano, after all. Ground zero isn't necessarily the beach, either, and any divine caster or alchemist of 12th level can handle radiation (PF treats it as poison). Of course, they'll be somewhat worse for wear, and there are demons about. The PCs also happen to be the only people trained in demon killing on scene who aren't dead or indisposed. Need to somehow get the demons dealt with so rescue forces can move in, then figure out exactly what just happened here.

[Ninjadeadbeard]

Need to somehow get the demons dealt with so rescue forces can move in, then figure out exactly what just happened here.

That sounds pretty cool. If I may though: Don't have them deal with the demons. The city's been nuked, which will probably hamper most of the players just in HP terms (let alone the rads), and then Demons attack? It should be clear to your players at this point that "Winning the battle is no longer on the table. Survival? Is." You could have a session where the PCs are trying to rally/protect survivors and reach a safe rendezvous point outside the city. Along the way they can dodge demons and irradiated debris, and occasionally jump a few weaker demons to save civilians. But a straight up fight? Save that for the counterattack.

I always wanted to have my players be repair droids on a mysteriously derelict space station/colony ship that suddenly activate...ten thousand years after launch. And no one was alive on board to wake them...

[The Glyphstone]

The city of Kym, sprawled across both sides of a river, is practically at war with itself. Each half is overseen by a Duke, both considering the entire city to be their rightful domain and the other duke as an usurper. The duke of the northern, older area is a brutal and cruel tyrant, a brilliant and treacherous political schemer but rather inept at both military and economic strategy. The southern, newer portion of the city is ruled by a kind and benevolent man whose only fault is being excessively trusting and naive. Once, he was an extremely skilled warrior, but since taking up the throne of his half of Kym he has become lethargic and apathetic. His only joy is eating the chewy sap of the bubali tree, a substance that agents of his rival managed to get him addicted to. Between the absence of leadership from the south and the inept brutality of the north, the entire city of Kym is on the verge of collapse in the face of raids and attacks by monsters and barbarian tribes.