Postbus trip over the Klausen Pass
F. Engesser
CC BY-SA 4.0
<bdi><a href="https://en.wikipedia.org/wiki/en:PTT_Archive" class="extiw" title="w:en:PTT Archive"><span title="company archive of PTT and historical archive of the Universal Postal Union (UPU) in Köniz in the canton of Bern, Switzerland">PTT Archive</span></a>
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