Mai oder Konrad reitet in die Südsee) is a novel by Erich Kästner, first published in 1932.

In his preface to the 1929 Emil and the Detectives the narrator recounts that he intended to write a humorous South Sea adventure story, but got stuck with the concrete details and finally followed the advice of a head waiter in his favorite cafe shop to write instead a book set in the familiar Berlin reality.

Several of the characters briefly mentioned where Kästner describes his aborted fantasy were taken up in "35th of May", written three years later.

One Thursday — it happens to be the 35th of May — they meet Negro Caballo,[2] a black horse that can speak, is well-versed in German literature, and at the same time, is the best roller skater in the world.

Together they enter Mr. Ringelhuth's huge wardrobe, which stands in the hallway, and end up in a series of magical lands, starting with the land of Cockaigne ("free entry — children half price"), followed by a medieval castle complete with jousting, an upside-down world in which children send bad parents to reform school, a science fiction nightmare city with mobile phones and moving walkways, and a South Sea island.