Opaka (Bulgarian: Опака) is a town in Targovishte Province in northeast Bulgaria. As of December 2009, the town had a population of 2,873 and covers an area of 57 km². It is 70 km south of the city of Rousse on the border with Romania and 250 km northeast of the Bulgarian capital, Sofia. Archeologists have found evidence of Thracian, Roman and Slavonic settlements in the area. Near the village of Krepcha, a stone monastery is the site of the oldest known Old Bulgarian Cyrillic inscription, dated from around 920 CE.