Brave Arthur and the Mysterious Castle

The book is a complete body. 

The main character is brave knight Arthur, who gave up his profession a long time ago and peacefully settled down on the edge of a forest. Unexpectedly he receives a parcel, which – as it turns out – is from the king himself. It is a letter asking for help to remove a spell from the castle. 

Arthur accepts the offer and sets off onto this difficult mission accompanied by his best friend – his always bored and yawning horse. 

Will he succeed in the mission ?