The Sostro District (Slovene: Četrtna skupnost Sostro) or simply Sostro is a city district of Ljubljana, the capital of Slovenia. It is the largest district of the capital and is located in the eastern part of Ljubljana. The area of Sostro is extensively forested and for this reason it is sometimes styled the "green lungs of Ljubljana." Historically, the wood from these forests was used for building houses, stables, and beehives, and as a basis for various crafts. Even nowadays, local people gather berries, mushrooms, and chestnuts here and sell them at the Ljubljana market.
Within Sostro, there are three main rivers: the Ljubljanica, the Sava, and the Kamniška Bistrica. They all meet at Podgrad. In the past, both the Ljubljanica and Sava were used for wood transport.
Near the village of Volavlje is Lehnjak Falls (Lehnjakov slap). This typical karst phenomenon is covered in moss.
Sostro also has apple, peach, cherry, and other fruit orchards. The local community organizes fruit festivals, the most popular being the Strawberry Festival in Janče.