So, I want to run a game, and running for these guys seems like the most likely outlet in the near future. But, with the restrictions above, most of the games/campaigns I'd want are right out. So, I was digging through my old box of ideas one time while walking the dog, and two ideas popped out, merged, and suggested some potential awesome.
Hail the Conquering Heroes
The campaign opens with the characters honored for remarkable heroics in the recent war to save the kingdom from the invading hordes of goblinoids led by a cabal of evil wizards. They aren't actually a party at this point. But, during the war, one frigate was blown WAY off course by a storm, and ended up discovering a hitherto unknown land. They camped on the coast for a while making repairs to their ship, and discovered that the land was good, and seemed totally uninhabited. The king wants to expand his territory to include this new country. As rewards for your bravery, the PCs have all been made lords and granted the right to claim as much land in the New World as they can control. If they prosper, the king has promised to grant them titles commensurate with their success.
The party is given three ships, a hundred or so colonists, and five hundred or so captured goblinoids as slave labor. They are also given a bunch of supplies, and the route to the New World. At this point, the players should be thinking that the campaign is largely about exploring and taming this new land while playing politics.
I Knew It Was Too Easy
Unfortunately for them, their promised land is, in fact, inhabited. Just not by humans, or even humanoids. Instead, it is inhabited by a strange life-form that the characters have never encountered before, and probably even the players have never even thought of. I'm riffing off of this awesome RPG.net thread. The natives of this new realm are, in fact, dungeons.
Dungeons are massive colony creatures, that have ridiculous levels of shape-shifting and mimicry abilities. It is perhaps incorrect to call the dungeon a creature itself. It is more like a bee hive or ant colony. But, the entire colony does act with remarkable coordination and interest in the welfare of the colony as a whole. The dungeon hollows out cave complexes in order to draw creatures in to feed on. There are several orders of creatures in the massive colony. At the lowest level are the dungeon "spores," which look amazingly like coins made of precious metals. The next level up are various oozes/jellies/etc. which act to clean, shape, and maintain the dungeon environment. Above that are a wide variety of creatures designed to use camouflage to lure people to their death. Yes, that would be the ancient classics of the trapper, cloaker, piercer, and other weird creatures that pretend to be dungeon dressing or treasure. Near the top of this hierarchy is the mimic, which is actually able to take on multiple shapes.
There are actually creatures within the dungeon which have independent brains. Kobolds and lizard-men share a certain symbiotic relationship with the dungeon. Doppelgangers act as independent agents of the dungeon, leaving its environs to explore the local area or communicate with other dungeons. And, in the very center, is the "queen bee" of the dungeon: the dragon. That huge pile of treasure the dragon sleeps on? That hasn't been carefully gathered and stored. The dragon actually generates that treasure, which gradually finds its way to the edges of the dungeon, and then out to the rest of the world.
So, it comes to light that one of these dungeons lives only a handful of miles inland from the new, fragile colony. In ways that are a mystery to be solved, the dungeon has structured itself to look perfectly like an old ruin from the Old World. And, now, the dungeon wants to consume the new colony. But, more importantly, it wants to send its seed across the wide ocean to establish colonies of its own....