Dragon Hill by Ángel Izquierdo

5.20

There are four entrances to the dragons' beautiful world: fire, water, earth and air. Only Ethelbert, the guardian, has the key and the secret to get out. Kevin, a boy form Mediaeval Age, falls into the water and goes to Dragon Hill. He and the youngest dragon become friends. But everything is not perfect in Dragon Hill. A mean wizard and his assistant are captured and try to make the boy let them free.