Rtanj is a mountain situated in eastern Serbia, approximately 200 km southeast of Belgrade, between the towns of Boljevac on north and Sokobanja on the south. It belongs to the Serbian Carpathians. Its highest peak is Šiljak, a natural phenomenon of karst terrain.

Sokobanja is a spa town and municipality located in the Zaječar District of the eastern Serbia. As of 2022, the population of the town is 7,188, while population of the municipality is 13,199.