Srebrna Góra, Poland
Fort Silver Mountain or Silver Mountain Fortress (Polish: Srebrna Góra) is a former mountain military fort built by the Prussian state, now a monument, museum and a huge tourist attraction for being the largest fortification of this type ever built in Europe.
The Silver Mountain Fortress is situated in the town of the same name, Srebrna Góra, in the Lower Silesia voivodeship around 80 kilometers from the province's capital Wrocław.
The fort was called Gibraltar of Prussia because it's built not on the surface of the Earth but in the solid ground, in the rocks of the Sowie Mountains.
The Silver Mountain fortress was built in the 18th century and because of the turbulent history of this land it has fallen to many hands including Prussian, Nazi Germany and Polish.
Now the fort is on the Polish soil, is very well maintained and was recently renovated and it's now open to the public so that tourists can visit it. For opening times and entrance prices please check the official website as these may vary from season to season.
Learn more about Srebrna Góra in Poland on Wikipedia