Our old farmhouse has been going up in dribs and drabs since 1867, and it shows. The basement alone has 1920s wiring going into a four-year-old furnace, with actual logs (some even have some bark on 'em!) supporting the ceiling over it. The plumbing and wiring range from "brand spanking new" to "old but fine" to "what the hell were they thinking?"
Just the latest example: the drain pipe from the bathtub was emptying directly into the crawlspace under the house. Thinking it was accidental, we of course fixed it. Turns out a section farther down the line freezes shut whenever it gets below zero outside, and some previous owner had disconnected it as a quick fix instead of shelling out the $20 a section of pipe heater would've cost. Oy.