Alejas iela 2, Dagda, +371 25727379, dean Pāvels Odiņš (+371 29583026).
Dagda Holy Trinity Roman Catholic Church is an architectural monument of national significance. It was built in 1741 in the Corinthian Baroque style. The church was founded by nobleman Jan August Hilzen (1702–1767). It features six magnificent altars, including three splendid masonry altars with cornices and pilasters. The main altar contains two paintings — one dedicated to the Holy Trinity and the other to the Immaculate Conception of the Virgin Mary. The church also has a baptistery decorated with gypsum figures.
Under the underground vaults of the church lie the burials of members of the Hilzen family — Jan August Hilzen himself, his son Justinian (a knight of the Maltese (Hospitaller) Order), and his grandson Idzi, as well as notable Dagda and Kaunata Jesuits Michał Rot (1721–1785) and Columban Pfeifer (1747–1798).
On the 11th day of each month at 11:00 a.m., a Holy Mass for the sick is held, praying for the health of soul and body. Water, salt, and medicines are blessed during the service.