Musical mystery

I walk (or run) up and down the Heiligenberg in Gensungen/Felsberg, Germany, where I live, almost every day and never fail to be surprised by something new, or something old seen in a new light.
The art trail throughout the forest is full of interesting surprises - Kunst aus der Natur versteckt in der Natur - and this is one of my favourite pieces. As I can't read music I often find myself wondering what the tune is. Is it a specific piece of music or simply random notes? Es ist ein musikalisches Geheimnis.