Lukina jama–Trojama

The Lukina jama–Trojama cave system lies in the Hajdučki kukovi area of Northern Velebit National Park. At 1,431 metres deep, it ranks among the world’s deepest pits, with its two entrances standing at 1,438 and 1,475 metres above sea level. Water corrosion and erosion enlarged tectonic fractures into a system whose lowest sections include horizontal siphon passages. Exploration in 2011 recorded ice as far as 560 metres below the entrances. This is protected underground terrain for specialist speleological research rather than a developed cave open to independent visitors.