The Karst Plateau separates Slovenia’s Adriatic coast from the mountains in the country’s interior. The limestone terrain of the area, which erodes easily, has led to the creation of interesting landscapes and given its name to other karst landscapes around the world. Among the most interesting features are sinkholes known in Slovenian as "vrtače."

Some of the sinkholes were created over the millennia as water eroded the local landscape. Others began their existence as caves that opened up when their ceilings collapsed. They vary in size, but the largest measure hundreds of meters in diameter and dozens of meters in depth. Depending on how they were created, some ore V-shaped, while others are U-shaped.

Regardless of their appearance, many of the sinkholes are characterized by unusually fertile soil. Because quality soil is otherwise rare on the Karst Plateau, many locals set up small plots of crops at the bottom of the sinkholes. They are also protected from strong Bora winds, which otherwise blow across the plateau; this even allowed vineyards to be grown in some of the “vrtače.” They have traditionally also been used as reservoirs, supplying much-needed water to villages on the relatively dry plateau during the summer months.

The largest also have their own microclimates. Frequent temperature inversions mean that air at the bottom is often colder than air at the top. Therefore, the “vrtače” function as frost hollows, with cold-resistant coniferous trees dominating their lowest points. Ice can last for weeks in the frost hollows, and for many years, local residents would cut the ice and sell it in the nearby port city of Trieste. Some villages even became famous for their ice-sellers.

The Karst sinkholes are no longer famous for their ice, but they are still an important part of the local landscape. Having shaped the local lifestyle for generations, they are now being discovered by visitors eager to explore the unusual landscapes and the history of Slovenia’s Karst region.