The Classical Karst, is as the name says, that area on earth where karst was first described. This area, owned by the Austrian Empire for centuries, was inhabited by the Slovene, one of so many peoples in this multi cultural empire. Trieste was the only mediterranean harbour of Austria, and so the road from Vienna through Maribor and Lujubljana to Triese was a very important highway. Many centuries ago, the first naturalists and geologists, geographers and historians started to describe the natural world instead of writing about alchemy and astrology.
And in this time, the area of the duchy Krain was decribed by Johann Weichard Frh. von Valvasor, a local aristocrat, who spent his whole possession to publish this book. The native language in this area was Slovene, but German was the official language of the Austro-Hungarian Empire. So he wrote his books in German, because he wanted it to be read by the German and Austrian scientists. It worked, the area called karst became well known, and its specialty and its name soon became synonymous, so the geologic term karst means every area which is similar to this part of Slovenia.
It is difficult to say which extension the classical karst has, the borders are not really well defined. Also, there are different interpretations, which parts of Slovenia to include. Geologically it is the area between the Ljubljana Marsh (Ljubljansko barje) and the Bay of Trieste. It has two different parts, divided by the European watershed Black Sea/Mediterranean Sea.
Part I is an area of high elevation along the Mediterranean Sea, from north of Trieste along Trieste and to the north of Istria is called Carso or Kras (Karst). It drains to the Mediterranean Sea. The Kras is a bare landscape, geologically called bare karst. But this was not all the time. During the ice age the climate was much cooler and wetter, huge forests grew in this area, and the soil produced by the dissolution of the limestone was covered and protected by the plants. When the Romans discovered that those forests had the longest known trees, they started to cut down the forest. The long trees were used for the mast, the rest of the wood for the rest of the ships. But as soon as the forest was missing, the sun dried the soil and killed the lower plants, and the soil without plants was eroded by every rain. Soon all the soil was gone and the area was a bare rocky desert. In other words the current barren landscape is a result of human intervention, an early nature destruction, which is under current climatic conditions irreversible.
The main cave system of the classical karst is the Reka-Timavo System. The Reka is a river from the Sneznik, the snow mountain, which reaches the limestone ridge of the Kras near Skocjan. Here it flows into the Skocjanske Jame. There are numerous daylight shafts and caves on the Kras which are tributaries to this system. In some caves the river reappears, and finally it springs as fiume Timavo, just to flow into the Mediterranean Sea after a few more kilometers. A huge part of the karst groundwater flows underground into the sea, so-called submarine karst springs.
Part II is located between Postojna and Ljubljana, and drains to the Black Sea. It is called the river with the seven names because it disappears underground and reappears various times. The locals were obviously not aware and gave each section a different name. And while the karst system is actually in the limestone ridges, where the river is underground, here is the list of the seven names.
The Reka-Timavo System is located in the Italian Friuli-Venezia Giulia region and the Slovenian Primorska. The Karst sytem of the Ljubljanica river is located in Notranjska and as a result often called Notranjski Kras.