I remember a momma opossum and some babies in a nest inside the chimney (closed off fireplace). Dad, grandpa and 1 uncle waited until the babies were big enough to survive without mom before having the chimney capped or maybe recapped.
Then there was the football-sized nest of yellowjackets that was behind a wall in the closet my sister & I shared.
As an adult, we've had ant infestations, mice and the odd bat find their way into the house. Mice were dealt with by traps, relocating or the cats. Ants? I had some kind of powder that basically desiccated them. I would put it in a thin line between screen doors and the inside doors and down the crack behind the kitchen counter. I was very careful where I put it as I didn't want the cats to be able to touch it. Now, I resort to ant bait traps again trying to make sure the cats can't get into them.
The bats? Last time we had one, probably 7 years or so ago; hubby got it out of the bedroom so we could sleep. When we got up the next morning, the cats were just laying staring at the little cat hideyhole. Similar to this just the bottom portion with the hole.
The bat was inside where it was dark.
Hubby picked it up and put it out on the porch (closest door) the bat flew off once it was dark outside again.