We knew that a building over one hundred years old may have some problems. There haven't been any major disasters yet but we have discovered some quirks and peculiarities in the "historic wing."
For example, the layout of switches and outlets is not always ideal. There is evidence of several pipes and wires and cables and switches that might have been functional at some point, but now they're capped or incomplete or missing or nonfunctional. The renovation left a mysterious gap between the old roof and the walls in the our wing that we'll have to investigate some day. Then there's the chandelier I installed in the dining room.
After it was all set up, we realized the fixture is connected directly to the house power, and the room's only light switch is apparently connected to... nothing. It's no big deal, though. I'll just go down to the basement and crawl into the cellar and turn the breaker on whenever we need light on the first floor. We can live with that.