It’s been 10 years since the first stamp on this subject: the series has previously featured highlights from the Bernese Oberland, the Appenzell region and Ticino. The new design takes us to a UNESCO World Heritage Site that uncovers the history of the Earth in a unique way. The border area of the Cantons of St. Gallen, Glarus and Graubünden is the location of one of the most primordial Alpine landscapes in Europe – the Tectonic Arena Sardona, which has been a UNESCO World Heritage Site since 2008. The remarkable thing about the area is the horizontal line running along the mountain peaks around Piz Sardona. The rock above the so-called “magic line” is older than the rock below it, when it should normally be the other way round. So are these mountains upside down? This phenomenon, which until recently was known among scientists as the “Glarus thrust”, is explained by the history of the formation of the Alps: when the continents of Europe and Africa collided, 250 to 300 million-year old rock met with a much younger substance. This produced a huge thrust that’s better seen in the Tectonic Arena Sardona than anywhere else in the world. This unique insight into the history of the Earth attracts researchers in the fields of geology and tectonics, as well as school visits and hiking enthusiasts. Another attraction is the Martinsloch, a 17-metre-high rock window on the Grosses Tschingelhorn mountain summit. Twice a year, in spring and autumn, this is the scene of quite a spectacle: for a few minutes, the sun shines through the Martinsloch “window” directly onto the church in Elm. This autumn, this natural spectacle can be seen on 30 September at 9.32 a.m. and on 1 October at 9.33 a.m.