Final farewell to Alexander Klimchouk, a leading researcher in Ukrainian and international cave exploration, the father of hypogene cave formation theory. Alexander Klimchouk recognized the importance of hydrogeology and basin-scale groundwater flow systems in cave formation processes. On this basis, he distinguished – according to the flow-system approach – the two main cave formation environments, epigene and hypogene. Alexander Klimchouk gave a short course on this topic at ELTE in 2012 and participated in the international symposium “Hierarchical Flow Systems in Karst Regions”, also at ELTE in 2013. His memory and professional work will stay with us forever.