Adds factory buildings you can walk into and build parts of your factory inside. This mod will not be updated for Factorio 0.15! Get Factorissimo2 instead, it's much better.
I accidentally tried putting concrete on the floor inside a factory and it let me. Admittedly this is a very minor bug. It seems like the movement speed is fast, like there is concrete. It's just weird that it let's you put down concrete.
