The Bergkirche was built in the early 18th century by Prince Paul Esterházy. Eisenstadt was the seat of the Esterházy family, and the church lies just short walk to the west of the family's main palace.
The Bergkirche is architecturally quite unusual and is built in two parts. The main section, the church proper, is approximately a square. The interior is in Baroque style. The ceiling takes the form of a dome, which was painted in fresco in the late 18th century.
A side chapel is dominated by a large marble sarcophagus, the tomb of the composer Joseph Haydn, who spent much of his career in Eisenstadt working for the Esterházys. The remains of most of Haydn's body have rested here since 1932; the skull was added (with due pomp and ceremony) only in 1954; for the reason for the disparity see Haydn's head.
The church still possesses its original organ, built in the 18th century by the Viennese maker Gottfried Malleck; the instrument has been restored to its original state, as it was when it was played by Haydn and Beethoven at the premieres of famous works. The original console, however, is no longer used but resides now in the nearby Haydn Museum.
References:The Clementinum is a historic complex of buildings in Prague. Until recently the complex hosted the National, University and Technical libraries, the City Library also being located nearby on Mariánské Náměstí. The Technical library and the Municipal library have moved to the Prague National Technical Library at Technická 6 since 2009. It is currently in use as the National Library of the Czech Republic.
Its history dates from the existence of a chapel dedicated to Saint Clement in the 11th century. A Dominican monastery was founded in the medieval period, which was transformed in 1556 to a Jesuit college. In 1622 the Jesuits transferred the library of Charles University to the Klementinum, and the college was merged with the University in 1654. The Jesuits remained until 1773, when the Klementinum was established as an observatory, library, and university by the Empress Maria Theresa of Austria.