Ključ Castle, Medieval fortress in Gacko Municipality, Bosnia and Herzegovina.
Ključ Castle is a limestone fortress complex in Gacko Municipality built on a high rocky hilltop, featuring a square main tower, defensive walls, and ramparts at an elevation of about 521 meters (1,710 feet). The remains are still visible today and show the construction methods and defensive layout of the medieval period.
The fortress gained regional importance in the early 15th century under Grand Duke Sandalj Hranic, who used it as a major administrative center and issued important documents from this location. It remained a key strategic position until Ottoman forces conquered it in 1463.
The site brings together multiple structures from different periods: the fortress itself, the town below, and a mosque with its women's quarters, showing how various communities shaped this location. Visitors can still see how these elements coexisted and reflect the layered history of the region.
The site is open to visitors but undergoes regular archaeological study, so some areas may be temporarily restricted. Wear sturdy footwear because the terrain is steep and rocky, with an uneven ascent to reach the site.
The last Bosnian king, Stjepan Tomasevic, took refuge in this fortress while fleeing advancing Ottoman forces before it fell in 1463. This moment marks a turning point in both regional and royal history.
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