1. Petrovaradin Fortress, also known as Petrovaradinska Tvrdjava, is a fortress located on the right bank of the Danube River in the city of Novi Sad, Serbia. It is one of the largest and best-preserved fortresses in Europe.

The fortress was built in the 17th and 18th centuries by the Austro-Hungarian Empire as a defense against the Ottoman Empire. It is famous for its intricate system of underground tunnels, which were used for military purposes during the Austrian rule.

One interesting fact about Petrovaradin Fortress is that it is known for its clock tower, which is the second largest in the world, after Big Ben in London. The clock on the tower is unique because it has shorter minute and hour hands, which were designed this way to prevent confusion among the sailors on the Danube River.

Another interesting feature of the fortress is the Petrovaradin Fortress Beach, located beneath the ancient walls. It is a popular hangout spot for locals and tourists, offering a stunning view of the Danube River and the surrounding area.

2. The working time of Petrovaradin Fortress varies depending on the season. During the summer months (June to August), it is open from 9am to 10pm. In the spring and autumn (April, May, September, and October), the fortress is open from 9am to 6pm. During the winter months (November to March), the fortress has shorter working hours, from 9am to 4pm.

Unfortunately, I couldn’t find a direct phone number for the fortress. However, you can contact the Tourist Organization of Novi Sad for more information at +381 21 6611 343.

3. Admission to Petrovaradin Fortress is free of charge. Visitors can explore the fortress on their own or join a guided tour, which are available for a fee. The fortress is easily accessible by public transportation, and there are several bus lines that operate in the area. Additionally, there are parking spaces available for those who prefer to drive.