Friuli Venezia Giulia is a region to the northeast of Italy, with borders to Austria and Slovenia. The south is flat with sandy beaches on the Mediterranean Sea, most famous is the city of Venezia (Venice). The north extends into the Alps, with mountains rising more than 3000 m asl. This area is divided into an eastern and western part by the huge river Tagliamento. To the east, around Trieste, is the border to the Slav world, with famous limestone karst.
The karst around Trieste is the Classical Karst, a large limestone plateau, which is heavily karstified. When the name was introduced, there was no border and all belonged to the Austro-Hungarian Empire. Today part of the karst belongs to Italy, the other part to Slovenia. The caves on both sides of the border are connected, at least sharing the same hydrological system. They belong to the Reka-Timavo river system.
The Reka river has its source at the feet of the highest karst peak, the Sneznik (Snow Mountain, 1,986 m asl). It crosses a low plain compsed of soft flysh rocks, before it enters the karst below Škocjan through the Škocjanske Jame. Several caves of this area show short pieces of the river course, for example the Grotta dei Serpenti, Abisso di Trebiciano and the Grotta di Gabrovizza. The Grotta Gigante also belongs to this system, although it is a much higher fossil level which is not connected to the deeper course of the river. Finally the water emerges in the Timavo resurgence and flows into the sea soon after.
But Friuli Venezia Giulia has more karst areas. There are several units of the southern limestone Alps on both sides of the river Tagliamento. The eastern part, around Udine has various caves, among them two impressive show caves. The eastern part around Gemona is infamous for the huge earthquakes which happen in this area rather often, in geologic terms. The last huge earthquake happened 1976.
In 1997 the cadastre of Friuli Venezia Giulia listed 6,073 caves, 3,311 in Friuli and 2,762 in Venezia Giuulia.