I understand the fuel concern, but I don't really think we should be so quick to settle down. It's far from certain that we have the best or even a particularly good tile at the moment; I'd keep exploring for a while longer while we still have a lot of time before being a nomad becomes a problem. Besides, if we settle down now, we'd have to start actually working to exploit our resources, so it's not like we don't have the same problem either way.
I do think the problem with fuel is mildly exaggerated given that we're cave people with sharp vision who don't actually need a huge, blazing fire to adequately light an area when a bed of glowing coals would suffice. Still, having thought it over, I can see doing things I was already thinking about in a different order to make it easier, so, people who like my campfire idea, but are worried about getting fuel first, how about the following as an Expansion proposal instead?
Rockbreakers
You learn a lot about rocks, living in the caverns. Each type of rock has its own individual color, texture, even taste. One thing you might notice, if you pay attention, is that some rocks are harder than others. Take one of those harder rocks, give it a bit of a point, and hammer it against a softer one, and the softer rock breaks. Do that for long enough against the places where the cave walls themselves are softer, and you get a hole. Thus, a new skilled trade is born. Though their work can be dangerous and is certainly exhausting, the Rockbreakers, considered by some the new specialized elite of our society, are the first of our kind since we delved into the dark to be able to go where they choose and not just follow the routes nature has carved — provided the mineral veins cooperate.
Just to give you an idea where I'm going with this so you can decide whether you like my vision, my Exploitation proposal for next phase would then be:
Black Gold
Our Rockbreakers reported back an interesting finding: a seam of dark rock with a gritty and almost greasy texture never seen before. It's not too hard to break chunks of this new rock out of the seam using our stone tools, and, as the Rockbreakers were playing around with it, a small accident unveiled something totally unexpected: the black rock burns. The very idea of burning rocks like wood, something we could hardly have imagined before, can only be proof that the gods smile on us down here and have provided us with underground equivalents to the things we could not bring with us from above. If we can find more of this new kind of stone, having the ability to build fires with more than just a few bits of lichen as fuel again will be the first step to making this hole in the ground into a home.
This gives us, I think, a pretty solid footing toward developing things like mining and smelting which we'll need to make the most of the wealth of the deep Earth. My nice campfire idea could then fit into Experimentation or wait for another phase.
I do have two concerns about this, though. One is mechanical, and I hope Paperman will weigh in on it: I'm not actually sure if proposing a new kind of resource is an Exploitation-phase project. To me, the rules about the exploitation phase seem to imply it could be, but maybe we are only meant to propose ways to get resources there. Given that I had previously been thinking of mining itself as an exploitation-phase project and I just rewrote it as what seems to me like a perfectly reasonable expansion-phase social development, I'm not sure how firm the boundaries between the phase types are.
My other concern is: we're going to have to make sure we have plenty of ventilation.