This is the region which borders Greece to the south, Macedonia, Serbia and Montenegro to the west and the northwestern part of the Stara Planina Mountains to the north.

The relief of the Southwestern Region has a variety of landforms - ridges, slopes, flat areas, river valleys, gorges, alluvial cones, circuses and others. The whole Rila Mountains falls into this region with its 2700-2900 m high parts and the highest peak on the Balkan Peninsula - Mussala of 2925 m height. The steep slopes are hard to reach but offer perfect conditions for tourism. Pirin Mountains has also some ridge parts of 2600-2900 m height. Both mountains are well-forested. Along their slopes there are vast highland pastures. Both mountains are rich in water resources.

The valleys are the most widely spread relief form in the region. They occupy 25% of the territory of the region. The most spacious among them are: the Sofia, Radomir, Kyustendil, Samokov and Razlog Valleys. The valley bottoms are flat and covered by diverse soils creating good grounds for the development of agriculture. The biggest settlements are also located here. The valleys of the Struma and Mesta Rivers are also large and fertile.

The climatic conditions of the Southwestern region are diverse. According to the climatic division of Bulgaria this region falls into three of the climatic zones - temperate, continental-Mediterranean and transitional-continental. All these zones differ in the average annual climatic characteristics of temperature, precipitation, air humidity and fogginess. The Struma, Iskar, Dzherman, Sandanska Bistritza, Eleshnitza and other rivers spring up from Vitosha, Rila, Pirin and Osogovo mountains. In this region are located all highland lakes of Bulgaria. In Rila the number of the circus lakes is 189, in Pirin - 176. They have an important bioclimatic significance. The Southwestern Region is rich in mineral springs. Most of the hot mineral springs are used for healing purposes. The most famous mineral springs of the region are: Bankya, Gorna Banya, Sandanski and Garmen.

Approximately 40% of the territory of the Southwestern Region is covered by forests located mainly in the Blagoevgrad and Sofia sub-region. There are both deciduous and coniferous forests. Due to the mountainous character of the region only 20% of its territory is arable land.

In this region are located five administrative regions - Sofia City and the Districts of Sofia, Blagoevgrad, Kyustendil and Pernik.