The Pavilion on Royal Hill is the only remaining Baroque building in the Castle Park with portraits of leaders of the Original Settlement and Hungarian kings. The hexagonal building, 200 meters from the castle, was built by Antal Grassalkovich I in the 1760's. In the 17-18th century, lodgings of lords were often made look like galleries. It was partly to express their nobility, partly to show their history in pictures.

The southern wing apartment of the Palace, which Antal Grassalkovich I rendered at the disposal of his friend, Count Kristóf Migazzi, Bishop of Vác and Cardinal Archbishop of Vienna, was converted into a theatre by Prince Antal Grassalkovich II between 1782 and 1785. The Palace theatre was opened earlier than the Castle Theatre that the Buda Carmelite church was converted into at the instigation of Farkas Kempelen in 1787.

Grassalkovich who came from a lower noble family and had an education in law, - as a result of his talent - completed a career rising high. He had an important in rising the Queen to the throne, since during the Austrian War of Succession (1740-48) it was Grassalkovich who organised the support of the Hungarian nobility. As a reward for the successful increase of the wealth of the chamber, Antal Grassalkovich the 1st was risen to the rank of a count by Maria Theresa in 1743, and also appointed as a secret councellor.