calzephyr | YA novel from the 80s (I think)

Book I want to read

Originally posted by

kayelledub at YA novel from the 80s (I think)

I'm looking for a book I read as a child in the 90s, but that I think was published in the 80s. It had a castle and a unicorn on the cover. I don't remember much of the synopsis but I know it was about siblings who had to go stay with their aunt and cousins (whom they did not like) for a summer and who found a portal into another world thru a shrub in the yard. The other world had unicorns and knights and the kids had to go on a quest.