Hisarlaka Fortress overlooks the town of Kyustendil from a hilltop 2 kilometres to its southeast, occupying an irregular polygonal area of approximately 2,000 square metres following the terrain's natural contours. Originally constructed by Romans around 400 AD, the fortress served as a major administrative and religious centre throughout the First and Second Bulgarian Kingdoms before suffering partial destruction by Ottoman forces in the 15th century. The substantial defensive structure measures 117 by 175 metres and features 14 towers of varying shapes—round, triangular, and rectangular—along with two gates and five barbicans, with walls up to 10 metres high and towers reaching 12 metres. Declared a cultural monument of national importance and accessible without entrance fees, Hisarlaka offers visitors historical significance combined with panoramic views over Kyustendil and its surrounding landscape.