Search the internet with a sample photo. But even that proved to be very difficult. I must have seen around 500 photos before I found what I looked for. The artwork is called "Needle tower" and made by a artist called Kenneth Snelson. There are 2 versions of this freestanding tower made with tubes and wire. Needle tower 1 is standing in Washington DC, USA and needle tower 2 stands in Otterlo, Netherlands.
More info on: http://en.wikipedia.org/wiki/Needle_Tower
I'm glad I found this finally as the QSL picture kept my mind busy. The designer of the card did a very good job as I'm certain I'm not the only one that wishes to know what it was.