I lived in a flat in a 200-ish-year-old building when I was at uni. Lovely flat, handy for uni, handy for work, near the shops, near a park, flatmates were pretty okay, comfortable, airy, well-lit, and warm.
Here's the thing we - a flat full of nerdy tech students - never figured out.
The walls in two of the bedrooms (including mine) were perfectly plumb, all four walls straight. Bookshelves lined up nicely with the walls. The floor was flat and level.
But the room was 10cm narrower at the ceiling.
Have you ever been to The Mystery Spot[1]? It is a fun tourist trap with all sorts of conundrums like that.
[1]: https://www.mysteryspot.com/
obviously a small space-time anomaly. Nothing to be alarmed about. Sapphire and Steel have been assigned.
This is the answer we came up with. Guy in the flat downstairs must have been dicking about with supermassive dark matter.