A system consists of a 8x10 hex map on which are randomly placed 20+1d10 worlds (well, mostly random — the rules stipulate that you can choose where to place the last 10 or so in order to make sure worlds have access to other worlds in a way that you want). Each world has several characteristics reminiscent of Traveller: Atmosphere, Temperature, Biosphere, Population, Tech Level and Tags. There are two big differences, however. Biosphere refers to how the native life relates to humanity and Tags are a plethora of descriptors that give depth and flavor to the world itself. The rules suggest two for each planet. Further, the descriptions of these Tags come with what are called Complications — what amount to campaign and adventure seeds.
Thus, I gleefully filled out a hex sheet with planets in order to flesh out the Black Reach Sector. The results were challenging — just the way I like them. The dice came up with three hive worlds which could be a stand-in for my version of the sector capital. However, one had a low tech level and another had the tag Xenophiles — hardly appropriate for a world that had just been decimated by an alien (ork) invasion.
This left me with only one candidate: Thick Atmosphere, Warm Temperature, Immiscible Biosphere, Population in the Billions (of course), a TL of 4 (which is Imperial normal), and has the Tags Floating Cities and Tomb World.
This implies that when colonists first arrived at Black Reach, they found an environment that was completely hostile to human beings — the atmosphere was too thick and the local flora and fauna were too toxic for human consumption. Their answer was to build a floating colony suspended in the upper (and therefore thinner) atmosphere where they could create their own (separate) ecosystem. This solution proved to be so wildly successful that the original floating colony grew to be one of many hive cities flying above a planet surface no human would think to set foot upon. As a result, no one realizes that Black Reach is actually a tomb world, where Necrons patiently await for a food source to awaken them from their slumber (and in turn, the Necrons have failed to awaken because the potential smorgasbord of all those hive cities are miles beyond their reach).
All of this also strongly suggests the reason why adventurers are needed on Black Reach. During the fighting of the ork invasion, the mechanism that kept one of the hive cities afloat was heavily damaged. As a result, the city descended onto the surface of the planet somewhat in tact.
Various factions from around the sector have become aware of one of several things that were in the hive city when it crashed to the surface. They are now in great need of expendable resources to descend onto the surface to recover these valuables (can anyone say tent pole megadungeon?)
The upside of this setup is manifold:
- I can justify a remnant ork population holed up in the hive city.
- Native flora and fauna can not only be found throughout, but be as wild, alien, surprising and toxic as I want them to be.
- Resource management becomes critical. The only food available is the food you bring in — even eating foodstuff found inside the city can run the risk of contamination. Filter masks are necessary to avoid having the air become toxic over time. Making sure the ride back home is secure becomes a real concern.
- The thick atmosphere justifies a constant fog of war — literally. Regardless of light source, line of sight is going to be severely limited.
- Has the hive city landed near a Necron tomb? Is there enough food that some have arisen from their slumber? If so, will an adventuring party inadvertently give them access to a transport to the billions who live above?
- Regardless of whether or not an adventuring party ever takes advantage of the Letter of Marque to go world hopping around the sector, this hive city, its denizens and the riches it holds will always be there to fall back on when a party wants a good, creepy and possibly rewarding adventure.