I've been reading through the Starfinder source book, Pact Worlds. It's a small book, but fits a lot of information into it, so I'm going to post about sections as I finish them.
Apostae is the twelfth celestial body (counting the Diaspora) from the sun in the Starfinder version of the Golarion system. There's no use in beating around the bush. Apostae is pretty much the Underdark. The planet has no atmosphere, so its surface is devoid of life and structures. Underground, though, is a network of constructed tunnels and caverns and cities.
Who else would you expect to find in the Underdark? Drow. Dark elves. That's the predominant race on Apostae.
I'm a big fan of Drow, thanks to RA Salvatore's Crystal Shard prequels. Honestly, I think an adventure in Drow society sort of just generates itself. Combine a little intrigue between opposing houses with a MacGuffin and you've got an instant heist or spy adventure. It's just such a rich story environment, I think this section could have been a page long and it still would have worked. Drow and futuristic underground city. Done.
And if that's not enough, then there are lots of excellent Drow adventures out there, including Rise of the Drow to Out of the Abyss. Sure, those are both for ancient D&D settings, but I'll bet it would be trivial to update them with sci fi weaponry.
Even so, this section does provide some key locations.
Crater Town is the half-orc colony. As far as I can tell, it's half shanty town, half military encampment. It consists of temporary pressurised shelters and mobile shelters, and I can imagine a few old spacecrafts positioned on the surface as functioning but flightless insta-cities. This all exists within a great crater on the surface of the planet, which as far as I can tell makes it exceptional in two ways. It's owned and managed by half-orcs, and it's on the surface and not underground.
Everything else exists underground.
Nightarch is the largest and most powerful city, with several Drow houses maintaining businesses and strongholds there. It's the major spaceport of the planet, so it's likely the first stop for player characters visiting Apostae. It's a sealed city, so you can walk around the streets without pressure suits, although House Zeizerer runs the Air services so how you go out at night largely depends on whether or not you trust them to maintain atmosphere.
Karkaken Test Ground is an area owned by House Arabani and is, as its name suggests, a test ground for the latest weapon tech.
Null Tracts is a stretch of tunnel that's entirely devoid of magic. No spell, magic item, or arcane effect functions within this region.
There's a university here, and a junkyard, dangerous crevaces and craters, factories, and encampments. Your players can explore this area for ages, and as long as you feel at home in the Underdark you'll have no trouble coming up with an adventure.
There's a player character theme at the end of the section. The Xenoarchaeologist character theme grants +1 INT, the ability to reduce the DC to identify rare alien tech. Later, you get the ability to spot traps and to translate languages. I find this theme puzzling, because there's not a whole lot about ancient Apostae in the section. This theme makes me think that this section was originally planned differently that how it ended up. Or maybe there are a bunch of notes about rare artifacts on Apostae that just didn't make it into the book. Anyway, it's a good theme, even though it has no obvious exclusive relevance to Apostae.
I've decided that the Starfinder worlds need shorthand descriptions, the way one might refer to Magic: The Gathering planes by theme. Innistrad is gothic horror world, Theros is Ancient Greece world, Ravnica is city world, and so on.
So far, this is what I have:
Next, and last in line, is Aucturn.
Header photo by Seth Kenlon, Creative Commons cc0.