Fort Punta Christo was built at the end of the 19th century by the Austro-Hungarian Monarchy to defend City of Pula, their main naval port. Situated on a small peninsula at 45 meters above sea level, Fort Punta Christo offers a breathtaking view of the entrance to the Bay of Pula, its breakwater, as well to National Park Islands Brijuni on the other side. The fortress is surrounded by a deep ditch and there are three entrances leading to the fort. Inside the fort are three courtyards through which you can enter the underground areas of this magnificent structure. The fortress has as many as 270 spaces, covering an area of over 10,000 m2.References:
The Petersberg Citadel is one of the largest extant early-modern citadels in Europe and covers the whole north-western part of the Erfurt city centre. It was built after 1665 on Petersberg hill and was in military use until 1963. It dates from a time when Erfurt was ruled by the Electors of Mainz and is a unique example of the European style of fortress construction. Beneath the citadel is an underground maze of passageways that can be visited on guided tours organised by Erfurt Tourist Office.
The citadel was originally built on the site of a medieval Benedictine Monastery and the earliest parts of the complex date from the 12th century. Erfurt has also been ruled by Sweden, Prussia, Napoleon, the German Empire, the Nazis, and post-World War II Soviet occupying forces, and it was part of the German Democratic Republic (East Germany). All of these regimes used Petersberg Citadel and had an influence on its development. The baroque fortress was in military use until 1963. Since German reunification in 1990, the citadel has undergone significant restoration and it is now open to the public as a historic site.