Cathouse
Here in northern Montana, the winters can get quite cold; -40º is not uncommon. In the local feral population, we were seeing loss of ears, tails, and deaths. All from cold.
So we built this:
That picture was taken before Halloween, the first year we had it up. Halloween is a US holiday in the fall, at the end of the month of October. So as you see, winter arrives with a bit of authority here.
Here's a summer image; you can see we added stained glass to the side windows:
In the winter, the second floor has a pad heater, a folded up comforter, and as you see, light. Access to the second floor is now via a folded baffle, which keeps the wind from constantly flowing about the upstairs.
On cold days, we can see them in there from our house, several all at once, all cuddled up together. What we can't do is approach them; they're gone before we can get anywhere near them. I keep hoping to get a shot with cats in the thing, but so far, no luck.
They shelter in there when it rains, too, which is fun to see.
We're in the process of building a second shelter; this one's going to be a castle. We call it a "catsle." We hope to have it all done before the end of this October. When we finish, I'll post about it.