www.slovenia-travel-guide.com Koper Slovenia Socerb castle. Socerb castle was built on top of a large rock, this medieval castle has an amazing sightseeing on the Trieste gulf, Koper bay and the valleys of Istria. Not far from it, a holy cave, the upper part of which is the only underground sanctuary visited by pilgrims. Socerb castle represents the unique standing fortification situated on the natural cliffs, which was once a political border between the Venetian Republic and Habsburg Monarchy. It had an important strategic and political function during medieval period. The castle formed part of the Venetian domain for only half a century. Mostly, it belonged to Austria and its margraves who, whilst living in the castle, substantially increased their power. For this reason, the castle represented an important military fort with permanently resident troops. It controlled a major trading route leading from the sea to the inland territories. Nowadays, the castle become as a state owned property of national importance.