What do you think of Factorissimo 2 and caves?
Minus steam engines, would it be possible to complete the entire game underground?
I haven't seen oil on the surface or in the caves, where is it supposed to spawn?
Is it possible to get power from underground to the surface?
The occasional water square spawns underground, is that supposed to happen?
If biters are turned off at generation but would normally spawn underground, where do they spawn?
Since cave exits can be spawned on resource patches, it is impossible to cover the very center square. Is there a way to fix this? Larger area mining drill mods don't exist.

This is even better than RSO in my opinion. :D

Never mind the biter question, they work as expected.
After turning the oil up to its max settings, I found some underground, maybe increase the spawning of oil, since it is probably getting covered by the underground walls.
In addition to some water, why do dirt tiles spawn underground?
Should Ion Cannons be able to fire underground, because I don't think so.
Are enemies able to expand underground?

Still better than RSO. :D

I haven't really thought of a cave only run yet. I think there are 2 things missing to do it: a lack of wood and water.
now you don't need much wood to finish the game, just for some poles, so that might not be a big issue, just something to work around (also bob's mods need wood automation...). Water however is currently not "really" generated in the caves. but ideally at some point i want to have that too, because it enriches the currently rather plain environment.
Currently power cannot be transferred from the cave to the surface. (as of now, it wouldn't make much sense, since there is no sun for solar, no space for nuclear, and no water for steam)

Oil generates in caves similar to other resources as well. The issue is just as you mention that the walls cover it quite often. this happens to small patches like uranium as well. I don't know yet how to prevent that. Personally i am playing with very big resource settings at the moment to avoid that. I am thinking of redistributing "lost" resources elsewhere, because currently that is too much luck based.

Occassionally some tiles end up not being overwritten in the cave, this is probably the water you saw, it can also happen to other tiles like dirt. It is a bug i have not yet found.

I think i can't do much about Ion cannons. i don't know how it is written, but i would expect somewhere a hard-coded list of surfaces would be required where to allow it or not. (does it fire in factorissimo's?)

I think biter expansion should be working in caves as normal, but i haven't checked it

Ion cannons can fire in Factorissimo.

This mod is better than RSO until you need 4 blue belt each of iron and copper ore, as snaking them around the place is a pain. Still great though. Maybe add a few wider corriders in each direction (NSEW) and call them lava tubes or abandoned mineshafts or something. That way, WE COULD STILL USE TRAINS! :D

Edit: What if you have a small surface operation to barrel water, 1 steam column on surface to run assembler + lasers, and everything else underground? I think Factorissimo buildings can output power.

Edit: Found a large mining drill mod (Omega Drills). This may help my belt navigation problems, and getting that pesky square under the cave exits. Found an oil deposit under cave exit. No large mining drill mods for that. :(

yes, i imagine the late game will be painfull (only reached the midgame myself yet)
i have yet to think how to deal with it. when i originally created the idea i thought of different cave levels, with the first one being poor quality, then regular, then rich. (uranium would only generate on the third...)
but during implementation that seemed to get too complicated so i discarded it for now. (especially since world gen is already affecting performance).

i think some corridors and occasional larger rooms would be very nice. but i think it will be a bit difficult...

i don't think i directly want to make the cave train compatible, i think that would cut a bit much into the cave. however i would like a subway mod, which the player could use to create a kind of public transportation system for players only. but i don't think i have the time to do it, if anyone wants to, feel free :)

yes probably you can already do it if you barrel the water. also you could belt solid fuel/coal to the surface for the power gen for lasers/assemblers.

i uploaded version 0.1.4, where you can place entrances. you can also deconstruct them so if there is one in the way, it should be possible to move it now.