Slovenia 2013, Caves of Postojna, 2 euro commemorative coin. In 2013, Slovenia will celebrate the 800th birthday of the discovery of the Postojna caves, also known as the Adelberg Cave. The caves of Postojna are a system of limestone caves, existing in three levels. The central image of the coin is a stylised spiral, which at the left side of the coin begins with inscription ‘POSTOJNSKA JAMA • 1213–2013 • SLOVENIJA’ and ends with two stylised speleothems. The coin’s outer ring depicts the 12 stars of the European flag. Number of coins to be issued: 1 million.