I too spent a long time thinking about this question. This is also the only card I have ever made (so be kind). I have visited all the world's previously mentioned and loved them. Hogwart's would be amazing. As would Wonderland, Ombra, Victorian England, Hobbiton, Rivendale, and Narnia. But in the end all of these were read long past my childhood. The world I remember amazing me when magic was real was Oz. I dreamed of
Spending a week working and playing alongside the Munchkins.
To be kissed on the forehead by Glenda.
Going on walks and picnics with Scarecrow, Tin Man, and Lion.
Seeing the Poppy fields and Emerald City.
Telling knock/knock jokes to the Guardian of the Gate.
Having campfire parties with the Winkies.
Fly with The King of the Winged Monkeys.
Thank you to @LizArnone for the wonderful and thought provoking question.