Vietnamese brigde in the István-lápai cave-Hungary

The István-lápa Cave was discovered in 1964 when a temporary sinkhole was opened; it is the longest known cave of the Bükk extending 4,100 m and is the country's deepest at 250 m. Its tiered shafts join the spatious level passage at deeper than 200 m. Its active western water-conducting branch is interrupted by siphons which are filled with water most of the year. Characteristics of its river bed are the fine solution pockets. The known part of its eastern branch is mostly an inactive upper level that joins the river passage with a deep pit. The lowest member of the system is the István Cave whose mouth is by the main road in the Szinva Valley. Most of the known passages of the 711 m long cave are also inactive; the developed section is popular among tourists.