A set consisting of a stamp and two coins
Postojna Cave boasts the world’s only underground post office, which was in operation between 1899 and 1945, and was listed alongside other global post offices. Its history has been commemorated with a miniature sheet with a postage stamp, which shows the post office. It was issued jointly by Pošta Slovenije (Slovenia Post) and Österreichische Post (Austrian Post).
Signatures have been present in the Passage of Old Signatures inside Postojna Cave since the 13th c