The Iglesia de Nuestra Señora de la Asunción dominates the Plaza de Cristo Rey with a well-proportioned Baroque facade that dates mainly from the 17th and 18th centuries, though the building incorporates much earlier medieval fabric. The interior has a single nave with lateral chapels, baroque retables, and a good collection of religious paintings and silverwork. The church was heavily damaged during the Carlist Wars of the 19th century and again during the Civil War, but it has been carefully restored.
The bell tower — square, solid, and visible from the surrounding countryside for a considerable distance — serves as the main vertical landmark of the village. Access to the church is variable; if it is locked, ask at the TIC on the plaza, which can usually arrange entry. The church is the focal point of Cantavieja's main festival, the Feast of the Assumption, held in mid-August, when the village fills well beyond its usual quiet.