Anyways, yesterday I had one of those cloudburst moments of creativity where it all just comes together at once after weeks of wracking my brain for ideas. It all starts with my brother-in-law's Christmas present to my son. Ammo Grot, as I like to call my son, is a pre-teen and into video games. My BIL decided this year to just give him for Christmas a dozen back issues of some video game magazine he has a subscription to. It sounds cheap, but it is actually brilliant. Tweeners are exactly going to be spending tons of money on cutting-edge games--they just want to look at pictures and read up on stuff and getting it all in one lump suits them just fine. Plus it is recycling. Win-win-win.
So I'm thinking to myself "what am I going to do for a story that isn't the same old monster lair raid" when I read an article for some video game from 2009 that was built around the idea of surviving a massive earthquake in the city. Ding! Here's the set-up: PC's are back in some major city doing their restocking/healing/etc. when the city is shook apart by a violent earthquake, leaving the party buried under a huge building. First, do the PC's dig upwards to the surface, risking having more of the building come down on top of them, or do they go downward into the city's sewer system and try to escape that way [Player Agency].
While digging they uncover an NPC, a young person whose father is a bigwig in town [roleplaying opportunity, minor quest--get the person back to daddy]. If they ditch the NPC, then they will have a more difficult time navigating the city since they are strangers to the area, not to mention losing out on the quest reward.
If they go down, they get a few sewer-based encounters [oozes, vermin, lycanthropes, maybe a hag as the BBEM] but also get a couple of clues from the subterranean denizens that the earthquake isn't natural. If they go up, they get to fight their way through the city [ghouls and carrion eaters, magical pets run amok, looters that could use the rarely-tapped PC race monsters from the Monster Manuals]. Either once back on the surface from the sewers or as they travel along the streets the PC's come across the residence of a local archmage that looks like it is in pretty rough shape: weird lights, sounds, etc. If the PC's investigate, they will rescue the mage who rewards them [Player agency, side small quest, maybe three encounters] and get another clue that the earthquake isn't natural but the result of something being summoned to the area [roleplaying opportunity].
The home of the NPC's father is also under siege, but after the PC's deal with that the father informs them (being a local scholar or sage) that an earthquake of this magnitude would be normally impossible and must suggest something is amiss [major quest: uncover (and hopefully stop) the cause of the earthquake].
Here's where I use what I call the "Quantum Ogre Theory" of gaming. If the PC's went into the archmage's house, then they already have some clue about what is going on. If they didn't, the NPC father can send them back to the archmage's house or to some other location where I recycle the encounters from the archmage's house (retooling them to be a library, a university, or a temple). At this point, the PC's can be pointed towards the location of the earthquake's epicenter and doubtless cause of the earthquake [something earth-related like a giant elemental or something]. But to get there they have to either a) travel below ground or b) travel through the city, whichever option they didn't take to get to the father's house, and I can recycle the encounters not used the first time.
This isn't really cheating your way out of Player Agency, it is just taking work you've already done and not inventing the same wheel twice. If I want I could make the quest to the summoned creature have a few more encounters [may want to see how long the game is going].
In the end, the PC's find and stop the creature, but then uncover mysterious clues to who might be behind the summoning in the first place. Is the city under attack from an unknown, perhaps subterranean power? Can we say Underdark?
Anyways, here's a rough map of the adventure, where you can see how it all ties together. My apologies for the terrible handwriting--I've suspected that I have undiagnosed dysgraphia.
As you can see, I need to do about seven encounters, plus maybe another three for the arch-mage sub-quest, and maybe a couple for the final search for the earthquake-causing monster. At a rate of gaming for three or four hours every other week, this should last me the better part of three gaming sessions or six weeks, minimum. All cobbled together in an hour, which is pretty cool.