Two books from my childhood (so, '70’s or earlier) that I want to remember so I can find them for my kids.
One:
A boy living in a remote household (in the Alps or similar, I think?) follows his beloved horse, who is near death, into the twelve houses of the Zodiac. If he can get round the whole Zodiac he can save the horse’s life. In the end he suceeds in his task, but chooses to let the horse die and become a chariot-horse in the sun’s chariot, rather than drag him back to an unhappy work-filled life on earth.
Two:
A book in which cats can find their way into other worlds by slipping through “gaps” in out of the way places which generally only they can see. Can’t remember another thing about it.