via: thisisbasel2.ch
A postcard or post card is a piece of thick paper or thin cardboard, typically rectangular, intended for writing and mailing without an envelope. Non-rectangular shapes may also be used but are rare. There are novelty exceptions, such as wooden postcards, copper postcards sold in the Copper Country of the U.S. state of Michigan, and coconut “postcards” from tropical islands.
Postkartenfestival: https://www.festivalpostcards.com/
Festival Postcards: https://www.festivalpostcards.com/
Carte souvienale set: https://fzco.ch/project/carte-souvienale/