The location of the package in Germany

This is the place where Adriaan finds the package and thus solves the riddle 'In the middle of the Rhine where singing was dangerous, Lamberti's rooster points from his throne where the package is'.

The throne refers to the Königsstuhl in Rhens and Lamberti's rooster appears to be standing on top of the Catholic Church of St. Theresia.
If you look in a straight line across both points, Marksburg Castle is indicated as the location of the package.