He was the founder of the International Sculpture Symposium. He held his first international symposium (Symposion Europaischer Bildhauer) with 8 participants in the old quarry Römersteinbruch in Sankt Margarethen im Burgenland. Prantl was invited to exhibit work in the Austrian Pavilion of the Venice Biennale in 1986.
Prantl died of a stroke at his home on October 8, 2010 at the age of 86.Wikipedia
All his life he has striven to break down barriers between different cultures and countries. This was particularly true during the fifties and early sixties when Prantl made contact with artists working in Eastern bloc countries, and established a series of stone carving symposia. This culminated in the development of the St Margarethen stone quarry Workshop in eastern Austria which acted as a catalyst for the organisation of many more symposia, often in troubled areas such as Berlin and the Israeli desert. [...]"(karlprantl.at)