The Karst Plateau or the Karst region (Italian: Carso; Slovene: Kras), also simply known as the Karst, is a limestone plateau region extending across the border of southwestern Slovenia and northeastern Italy.he Karst Plateau or the Karst region (Italian: Carso; Slovene: Kras), also simply known as the Karst, is a limestone plateau region extending across the border of southwestern Slovenia and northeastern Italy.