10 of the world’s most amazing caves to explore - SilverKris
"Inscribed as a UNESCO World Heritage Site in 1986, this impressive Slovenian cave system contains evidence of human inhabitation going back around 10,000 years and features one of the world’s largest known underground canyons, the Big and Little Collapse Dolines (where the entrance lies), rimstone pools and even underground waterfalls—making it a must-see for visitors to Slovenia." - SilverKris