Today I begin an artistic tour of the Rhein river, from art postcards purchased by a relative during a European vacation in 1930. Presumably, all the images date from at latest the 1920’s, but given they are artworks, could be significantly earlier. The physical cards themselves, however, are 1930 era.
The first place is Rheinstein Castle.

The back of the card has a legend in German, translated (poorly) as:
A jewel of the German past is Rheinstein Castle, like the nest of a bird of prey on a narrow, steep cliffs, rising high above the flowing waters of the Rhine.
It is number 93 in the series.