Topography of Croatia is defined through three major geomorphological parts of the country. Those are the Pannonian Basin, the Dinaric Alps, and the Adriatic Basin. The largest part of Croatia consists of lowlands, with elevations of less than above sea level recorded in 53.42% of the country. Bulk of the lowlands are found in the northern regions of the country, especially in Slavonia, itself a part of the Pannonian Basin plain. The plains are interspersed by the horst and graben structures, believed to break the Pannonian Sea surface as islands. The greatest concentration of ground at relatively high elevations is found in Lika and Gorski Kotar areas in the Dinaric Alps, but such areas are found in all regions of Croatia to some extent. The Dinaric Alps contain the highest mountain in Croatia— Dinara, as well as all other mountains in Croatia higher than . Croatia's Adriatic Sea mainland coast is long, while its 1,246 islands and islets encompass further of coastline—the most indented coastline in the Mediterranean. Karst topography makes up about half of Croatia and is especially prominent in the Dinaric Alps, as well as throughout the coastal areas and the islands.