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.
It appears that your save is corrupt somehow. I'm not convinced this has anything to do with Factorissimo in particular, since mods have no access to the savefiles, and even so I can't help you fix your save. Do you have an autosave of your world?
