A fire can be placed on solid land, or anything built with stone. make sure to either find a safe way to trap the smoke, or vent it out. use a roof piece to direct the smoke out if you decide to build a chimney. the entire chimney has to be at least 2mx2m wide (the width of a wall.) else the smoke will not escape through what looks like a perfectly sized hole. (this means placing a beam or pole in the middle of the exit will block the smoke. the particles are pretty big.)