The karst spring "Zhitolub" is located at the foot of the Lakatnik (Milanovo) Rocks, under the "Temnata Dupka" cave, about 8 meters above the level of the Iskar River.

The spring is one of the largest karst springs in the country and is formed by the confluence of two underground rivers — Petrenski Dol and Proboynitza. They pass through the water floors of the "Temnata Dupka" cave and through a narrow siphon flow into the spring, from where the water flows into the Iskar River.

The length of the tributary is about 59 meters, which is why it is often defined as one of the shortest rivers in Bulgaria. During heavy rains, up to 1200 liters of water per second pass through it.

The place is small but interesting and is often visited as part of a route in the Lakatnik and Milanovo area.