Unterground World

[Nexarius]

I think it would be cool if there would be an unterground world added to the game.

The unterground world would be basically a world that you have to excavate first (after mid to lategame research) to build anything and of course solar panels wouldn't work.
To switch from overworld to the unterground world there would be elevators which would work like the factorissimo building where you just have to walk into them and you are undeground.
In addition there would be several items that could interact with the underground.

These are some of the features that would be pretty cool:
Deep Power Poles to connect the overworld and underground electric grid.
Train tunnel entrance for trains to go underground.
There would be underground lakes but also lava lakes, caves with enemies and of course ore deposits.
Underground belts and pipes would have their counterpart in the underground world and you could change them however you want.