Croatia is a sovereign state at the crossroads of Central Europe, Southeast Europe, and the Mediterranean. Its capital cityis Zagreb, which forms one of the country’s primary subdivisions, along with its twenty counties. Croatia covers 56,594 square kilometres and has diverse, mostly continental and Mediterranean climates. Croatia’s Adriatic Sea coast contains more than a thousand islands. The country’s population is 4.28 million, most of whom are Croats, with the most common religious denomination being Roman Catholicism. Croatia can be subdivided between a number of ecoregions because of its climate and geomorphology. The country is consequently one of the richest in Europe in terms of biodiversity. There are four types of biogeographical regions in Croatia—Mediterranean along the coast and in its immediate hinterland, Alpine in most of Lika and Gorski Kotar, Pannonian along Drava and Danube, and continental in the remaining areas. One of the most significant are karst habitats which include submerged karst, such as Zrmanja and Krka canyons and tufa barriers, as well as underground habitats.