Târgu Ocna (alternative spelling Tîrgu Ocna, Romanian pronunciation: [ˌtɨrɡu ˈokna]) is a town in Bacău County, Romania, situated on the left bank of the Trotuş River, an affluent of the Siret, and on a branch railway which crosses the Ghimeş Pass from Moldavia into Transylvania. Târgu Ocna is built among the Carpathian Mountains on bare hills formed of rock salt. In fact the English translation of Ocna is salt mine.