The picture shows a view of the Lake of Lucerne from the Swiss village of Weggis. In Susan Interferes, the Carmichaels and Susan stay in the village of Rosendorf, a thinly disguised Weggis. In Susan and Friends, Beverley Garmston explains that Weggis is situated right where Rosendorf is located. The famous Weggis Rose Festival began in 1926 and this may have inspired Jane Shaw to call her ficitonal town "Rose Village", the translation of Rosendorf. Furthermore, Uncle Charles tells the children that there is a monument to Mark Twain in the village. There is indeed such a monument in Weggis, which you can see below. The famous writer described Weggis as "the most charming place for repose and restfulness". For further information, see Susan and Friends, Chapter XXI, Adventures in the Alps.