I feel your pain. 140 year old house with 3 additions and several remodels over the years. Still had a coal cistern when I moved in!
The middle bedroom has a partial window where the addition was tied in but they couldn’t be bothered to seal up the hole fully.. it’s about 8 inches wide and made of a custom storm window and nothing else (currently sealed up well with insulation until I can re-do siding).
Fireplace hearth (way overbuilt thing for a pellet stove -previous owner was a mason) was installed over a layer of hardwood flooring, which they didn’t realize wasn’t subfloor because there were 2 layers of hardwood flooring, old kind that was thick - the house sighed with relief when I ripped it all out and I gained 4 inches to my ceiling height.
Had to drill through a 4-inch thick cement wall to install my dishwasher. Someone moved the entry from one side to the other at some point, probably when they added the driveway and garage, and the walkway is still under my lawn. And my cabinets are different internal heights for some reason?
Weird stuff. Every project becomes 5-15 projects to do right.