This one-off adventure is easy to port in about any sci-fi world (or even fantasy-sci-fi world), but its feel is perfect for the Ninth World.
It is an underground story linked to a lost civilization, a huge, ancient juggernout used for a task not contemplated in its duties and two very peculiar communities of strange creatures fighting each other deep down underground.
What I loved of this adventure is not only how its background was built (the underground creatures are very alien in their organization and behaviour, but still everything makes sense once you understood them: there is no "weird for the sake of just being weird") but even more how understanding the background leads you to a maze of moral choices. This should be what sci-fi is for.
Considering the very low price and how this scenario can be very successfully adapted to about any campaign, I warmly recommend this adventure.
[5 of 5 Stars!]