Fortress "Petrich Kale" (or "Petricha") was an important fortress in the defense system of the medieval Bulgarian state. It is located 4 km.north of the village of Avren and a 1 kilometer east of the the railway station of Razdelna on Varna-Sofia railway line. The castle dates from the V-th century but for a certain period was destroyed and rebuilt again in XI-XII century.
In addition to Bulgarian, the "Petrich Kale" fortress is associated also with the Czech, Polish and Hungarian history. During the last crusade the United Christian armies under the leadership of the Polish-Hungarian king Vladislav III Jagiello Varnenchik on November 7, 1444 the fortress was conquered and destroyed.
The place is attractive for tourism and there is a tourist lodge built nearby. The rocks near the fortress are excellent for mountaineering and climbing.