You can do ethernet cables outdoors from your router in your house to your router in your office. Either thin cables that go under doors, or outdoor rated ones, both can work fine.
This same approach can work inside a house as an alternative to mesh networking or running cables through walls. The cables don't have to be invisible (underground or in walls) when you have tough constraints, unless you want them to be.
And then there are still those six feet of stone that needs drilling through to get the cable outside and back in.
Search for "cable protector ramps"
> And then there are still those six feet of stone that needs drilling through to get the cable outside and back in.
Thin cables designed to run under doors or windowsills are an option. Search for "flat ethernet cable"
It seems like you prefer your setup for good reasons, and these solutions above are both ugly, but I still wanted to note to others reading this that workarounds exist.
It's just that almost anything is better than wifi in concrete/stone houses. I can see point-to-point outside with an unobstructed view being reliable enough. But point-to-point through 3ft of concrete is [HN is a neglected Xennial hobby and doesn't support emojis]!
Certainly worth reconsidering wired when that P2P hardware goes EOL.