Exactly ten years after the recording of Felix Baumgartners base-jump in the Mamet Cave went around the World, this abyss on Velebit Mountain became the scene of another incredible daredevil venture. Ivan Trifonov, a seventy-year-old Austrian with a Croatian passport, was the first man to try, and succeed in flying a hot-air balloon underground. This experienced hot-air balloon pilot is already a proud holder of 4 Guinness records, and flying into the Mamet Cave, touching it’s bottom and successfully flying out of the Cave is likely to be his fifth record, since no-one has ever done such a thing before. For flying underground Trifonov had to use a hot-air balloon specially designed for this unusual, and probably unrepeatable venture. His balloon was smaller than usual, and the brave pilot set on two gas tanks linked with steel pipes, instead of a basket.