. . . was a stop on the train trip to visit grandfather for Rickie and Ann. And a proper destination for all children, it will seem to young readers -- for there the children do grown-up work while the oldsters play and school is a treat where one learns forgetting. In the hotel in Upside-Down Town the floors descend into the earth and the pillow goes at the foot of the bed. Even illness is fun, for the doctor prescribes only delicious pills on the first visit, with less tasty ones on return trips. Baseball games are won by the team which scores the fewest runs. Louis Slobodkin's insouciant illustrations in red and black complete an airily concocted trifle for easy reading. Side-sewn. Part of the fun is the fact that a bit of the text is upside down as well -- a gimmick which should appeal to some youngsters.