Przemyśl Fortress was built by the Austro-Hungarian Empire as a vast defensive ring around the city. In the First World War it became the scene of one of the eastern front's major sieges, then was deliberately damaged as the defenders surrendered.
The forts are spread across the hills, so this POI marks the Salis-Soglio area rather than the whole system. Go with a map, proper shoes, and daylight. The ruins are atmospheric, but they are not polished museum pieces.