Here is a rock that I have had in my basement since summer. It has finally made it to Forum members to voice their opinion on. I know it is NOT a rugosa coral (a joke for those who saw my previous ID request). I am thinking possibly a stromatolite? Or because of the karst topography in the region, it may be a type of flowstone from a cave. Or maybe one of those rocks to put out in the garden.
The bottom of the specimen:
The top:
Side views: