Ptuj Castle, also known as Ptuj Castle Hill or Ptuj Old Castle, is a castle located on a hill overlooking the town of Ptuj in northeastern Slovenia. It is one of the most prominent landmarks of Ptuj and one of the best-preserved castles in Slovenia.

The castle was first mentioned in the 12th century and has been rebuilt and renovated several times over the centuries. It has been owned by various noble families throughout its history, including the Counts of Celje, the Habsburgs, and the state of Yugoslavia.

Today, the castle houses the Ptuj Regional Museum, which features exhibitions on the history and culture of the region. Visitors can explore the castle's many rooms and halls, including the Knights' Hall, the Chapel, and the Dungeon. The castle also has a courtyard, a tower, and a drawbridge.

The castle's architecture is a mixture of different styles from different periods, including Romanesque, Gothic, Renaissance, and Baroque. The castle's exterior walls are adorned with decorative stonework, and its interior features frescoes, sculptures, and other artwork.

The castle is a popular tourist destination in Slovenia and is often visited in conjunction with a trip to the nearby town of Ptuj, which is known for its medieval architecture and rich history.