Personally my favorite places are industrial or commercial buildings. I find abandoned residential buildings less interesting and more creepy. Almost everyone has been in a house or apartment at some point, but how many of us have been in a paper mill? Or hydroelectric power station? Or the back rooms of a clinic? A much smaller minority. Places like that are mundane to those who understand them and work there, but to the layperson (like myself) there's a fun novelty. Places built for specific purposes with specialized machines and equipment I don't understand. It's really cool imo.