Sofia Valley in the context of "Burel Valley"

Sofia is the capital and largest city of Bulgaria. It is situated in the Sofia Valley at the foot of the Vitosha mountain, in the western part of the country. The city is built west of the Iskar river and has many mineral springs, such as the Sofia Central Mineral Baths. It has a humid continental climate.

Known as Serdica in antiquity, Sofia has been an area of human habitation since at least 7000 BC. The recorded history of the city begins with the attestation of the conquest of Serdica by the Roman Republic in 29 BC from the Celtic tribe Serdi. During the decline of the Roman Empire, the city was raided by Huns, Visigoths, Avars, and Slavs. In 809, Serdica was incorporated into the First Bulgarian Empire by Khan Krum and became known as Sredets. In 1018, the Byzantines ended Bulgarian rule until 1194, when it was reincorporated by the Second Bulgarian Empire. Sredets became a major administrative, economic, cultural and literary hub until its conquest by the Ottomans in 1382. From 1530 to 1836, Sofia was the regional capital of Rumelia Eyalet, the Ottoman Empire's largest and most important province. Bulgarian rule was restored in 1878. Sofia was selected as the capital of the Third Bulgarian State in the next year, ushering a period of intense demographic and economic growth.

The Iskar (Bulgarian: Искър, pronounced [ˈiskɐr]; Latin: Oescus) is a right tributary of the Danube. With a length of 368 km, it is the longest river that runs entirely within Bulgaria. Originating as three forks in Balkan's highest mountain range Rila, the Iskar flows in a northern direction until its confluence with the Danube. As it flows northwards it fuels the largest artificial lake in the country, the Iskar Reservoir, forms the divide between the Vitosha and Plana Mountains in the west and the Sredna Gora mountain range in the east before entering the Sofia Valley, which contains the nation's capital Sofia. From there the Iskar runs through the Balkan Mountains, forming the spectacular 84 km long Iskar Gorge. As it crosses the mountains, its water course turns in a north-eastern direction at Lakatnik. North of the Balkan Mountains, the river crosses the Danubian Plain and finally flows into the Danube between the villages of Baykal and Gigen. Geologically, Iskar is the oldest river in the Balkan Peninsula.

Its watershed drains 8,617 km in the provinces of Sofia, Sofia City, Vratsa, Lovech and Pleven. The Iskar flows through nine towns and numerous villages. The Iskar river basin is home to more than 50 species of fish, including Cottus haemusi that is endemic to the upper Iskar and Vit drainages.

The Sub-Balkan Valleys (Bulgarian: Подбалкански котловини, romanized: Podbalkanski kotlovini) are row of 11 valleys running from the Bulgarian border with Serbia east to the Black Sea. They are separating the Balkan Mountains from a chain of other mountains known as Srednogorie which includes Vitosha and Sredna Gora. There is great abundance of mineral waters. They are divided into two parts: Western (higher) and Eastern (lower). The western valleys include: Burel Valley; Sofia Valley; Saranska Valley; Kamarska Valley. The eastern valleys are: Zlatitsa–Pirdop Valley; Karlovo Valley; Kazanlak Valley; Tvarditsa Valley; Sliven Valley; Karnobat Valley; Aytos Valley.

The Stolichna Municipality (Bulgarian: Столична община, romanized: Stolichna obshtina (also transcribed as Stolična obština), lit. 'Capital Municipality') is an obshtina (municipality) in Sofia City Province, Western Bulgaria.It is named after its administrative centre, the city of Sofia, which is also the capital of Sofia City Province and Sofia Province and the capital of Bulgaria as well.

The municipality is located mainly in the Sofia Valley, and also in the feet and lower parts of the mountains of Stara planina and Vitosha, Plana, Lozen, Rila. As of 2016, it was home to 1,500,927 inhabitants, of which 1,400,000 live in Sofia.

Southern Bulgaria (Bulgarian: Южна България, Yuzhna Balgariya) is the southern half of the territory of Bulgaria, located to the south of the main ridge of the Balkan Mountains which conventionally separates the country into a northern and a southern part. Besides the Balkan Mountains, Southern Bulgaria borders Serbia to the west, North Macedonia to the southwest, Greece to the south, Turkey to the southeast and the Bulgarian Black Sea Coast to the east.

Geographically, the terrain in Southern Bulgaria is much more varied than that of the north, with the Upper Thracian Plain stretching in the east, while the south and west are dominated by some of Bulgaria's highest mountains such as Rila, Pirin and the Rhodopes, as well as smaller and/or lower mountains and valleys in the west, such as Vitosha, Belasitsa, Osogovo, the Sofia Valley, the Sub-Balkan valleys and the Kraishte region. Southern Bulgaria covers an area of 62,414 square kilometres and has a population of 5,085,872 as of 2009 (63% of Bulgaria's entire population), with a population density of 81.5 people per km. The three largest cities are the national capital Sofia, the largest city in Thrace, Plovdiv, and the major Black Sea port of Burgas.