Vrtiglavica, also Vrtoglavica (both from Slovene vrtoglavica 'vertigo'), is a karst shaft on the Kanin Plateau, part of the Kanin Mountains, Western Julian Alps, on the Slovene side of the border between Slovenia and Italy. It has the deepest single vertical drop in the world, at . The cave formed in a glaciokarst landscape; that is, a karst landscape that was subjected to Pleistocene glacial activity.