The relief of Bulgaria is diverse, including vast lowlands planes, low hills, high and low mountains, valleys, river basins and deep gorges. The surface structures were formed during different geological eras. Oldest in terms of geological classification are the Moezian Platform (the Danubian Hilly Plane) and the Rila Massif and the Rhodopes. The undulating system of Stara Planina and Sredna Gora mountains and the Sub-Balkan Valleys date from a later geological age.
     The average altitude of Bulgaria is 470 m. Over 2/3 of the territory is situated at an altitude of 600 m, i.e. lowlands, planes and low hills prevail. The lowlands (up to 200 m) take up 30 % of the territory, the planes and the low hills (200-600 m) - 40 %, the low mountains (600-1000 m) - 16 %, the medium high mountains (1000-1600 m) - 10 %, and the high mountains (over 1600 m) - 4 %. A typical feature of the relief is that its structural units alternate from North to South and extend (also diminishing in height) from West - North-west to East - South-east.
     In the northernmost part of Bulgaria, to the south of the Danube River, lies the Danubian Hilly Plane, the largest plane in the country. To the south it reaches the Fore-Balkan, to the west - the Timok River, to the east - the Black Sea. Its highest point (502 m) is in the region of the Shoumen Plateau. From the east to the west the relief changes from lowlands-plateau to uplands-plateau.
     The Fore-Balkan is a fore mountain of Stara Planina, from which it is separated by a system of gorges, defiles and valleys. It lies to the south of the Danubian Hilly Plane stretching from Vrushka Chouka Hillock to the Black Sea. The mountain rises to its highest point in the Vasilyovska Mountain - Vasilyov Peak (1490 m), and its average altitude is 364 m.
     The mountain range of Stara Planina lies between the Belogradchik Pass and Cape Emine on the Black Sea; to the south it borders on Sofia Valley and the Southern Balkan Valleys. Its length is approximately 530 km, its width - 15-20 km and its medium altitude - 722 m. The range reaches its highest elevation in the Troyan-Kalofer Mountain - Botev Peak (2376 m).
     Sredna Gora Mountain lies to the South of Stara Planina and almost parallel to it. It is connected to Stara Planina by means of the cross-thresholds Gulubets, Koznitsa, Krustets and Mezhdenik. Its length is about 285 km, its width - 50 km and its average altitude is 608 m. Its highest point is Golyam Bogdan Peak (1604 m).
     Between Sredna Gora, the Rila Massif and the Rhodopes there lie the low mountains Golo Burdo, Chirpan Hills, the massive mountain domes of Vitosha and Sakar, the isolated hills of Sveti Iliya, Manastir, Bakadzhitsite, etc. The upper Thracian and Bourgas valleys, the valleys of Pernik and Radomir lowlands are situated between these hills.
     The Rila-Rhodopes Massif consists of the Rila Mountains (highest point - 2925 m), Pirin, the Rhodopes and the mountain group of Osogovo-Belasitsa, which are the highest on the Balkan Peninsula.
     In the Quaternary Rila and Pirin were covered with glaciers; at an altitude of 2200 m numerous cirques, glacial planes, moraines and beautiful cirque lakes can be found. The sharp rocky peaks lend these mountains an alpine view. The mountain massif of the Rhodopes has almost square outlines and levelled ridges. It is characterized by the alternation of high long rising grounds and narrow valleys and ravines. There are numerous karst formations - caves, gorges, rock phenomena (in the regions of Trigrad, Velingrad, Dobrostan, Peshtera and Arda).
     In the eastern part of Bulgaria, by the Black Sea Coast, there are well outlined wide beaches. They occupy approximately 130 km of the Bulgarian Black Sea coast (378 km). The Kamchiya-Shkorpilovtsi Beach Line is the longest (12 km) one. The beaches are wide and covered with white and yellow fine sand.