This seems like a really fun and original concept, very very few mods have explored underground ideas so far! I would love to see this finished. Will you end up locking special resources below ground or just have it as an optional challenge that allows easier resource gathering? I also want to know what kind of dangers will be in the caves, for example will there be cave ins or a temperature or just plain biters? Whatever it is it would be awesome. Can't wait to play this.

Hey!

Yeah I should probably add a lot of my plans to an FAQ or something so people have an idea of what I'm wanting to do. I'd like to keep things pretty vague to not spoil anything but I will say that some of the plans so far include: locking specific resources behind specific underground layers/technologies, logistical challenges that stem from having factories across different surfaces, as well as physical threats similar to those you mentioned (perhaps biters, gas, other scary things). I will also mention that I don't plan on the underground being optional if you want to beat the game.

Thanks for the interest! Feel free to join the discord if you want to keep an eye on my progress ;)

Can you put a few screenshots though please?

Definitely! I'll take some time one of these days to add some.