The ornate white (er, sooty white) steeple of the Matthias Church is the highest point on Castle Hill. It was added in the 15th century, above a 13th-century Gothic chapel. Officially the Buda Church of Our Lady, it has been known as the Matthias Church since the 15th century, in remembrance of the so-called "just king" who greatly added to and embellished it during his reign. Many of these changes were lost when the Turks converted it into a mosque. The intricate white stonework, mosaic roof decorations, and some of its geometric patterned columns seem to suggest Byzantium, yet it was substantially rebuilt again in the neo-baroque style 87 years after the Turkish defeat in 1686. One fortunate survivor of all the changes was perhaps the finest example of Gothic stone carving in Hungary, the Assumption of the Blessed Virgin Mary, visible above the door on the side of the church that faces the Danube.

The Szentháromság Kápolna (Trinity Chapel) holds an encolpion, an enameled casket containing a miniature copy of the Gospel to be worn on the chest; it belonged to the 12th-century king Béla III and his wife, Anne of Chatillon. Their burial crowns and a cross, scepter, and rings found in their excavated graves are also displayed here. The church's treasury contains Renaissance and baroque chalices, monstrances, and vestments. High Mass is celebrated every Sunday at 10 AM, sometimes with full orchestra and choir -- and often with major soloists; get here early if you want a seat. During the summer there are usually organ recitals on Sundays at 7:30 PM.