There is little left of the original church built in medieval times due radical modifications carried out between 1535 and 1550. This mainly affected the roof structure of its only nave which became A-framed and is decorated with coffers and rosettes. The cross beams and the ceiling edge are decorated with winged cherubs. Finally, the corbels on which all the above elements rest, are beautifully carved. Other works of skilled woodcarving can be observed in the wooden balustrade of the choir gallery at the western end of the church.

The sacristy and the chapels of St Sebastian and of the Virgen del Rosario (Virgin of the Rosary) were also built in the 16th century. In 1756, one of the most unusual elements was added to the structure of the church - a chapel dedicated to the Virgen del Arco (Virgin of the Arch) and open to the street.

Inside the church and particularly worthy of note is the main altarpiece, a Romanist work built between the end of the 16th and beginning of the 17th centuries. It is dedicated to St Anne, San Juan Evangelista (St John the Evangelist) and Santiago el Mayor. The centre of the altarpiece holds the sacrarium, a free-standing piece with two levels and a domed roof. On either side of the sculpture of St Anne is the first level of frescoes.

The altar piece dedicated to St Sebastian is also of great artistic value. It was finished in 1531 and is presided by a sculpture of the saint made by two masters from Sangüesa (Navarre), the stonemason Joan Charles and the painter Anton (possibly Anton de Arara). Experts point out the evident influence of Durero engravings in the design of the panel paintings. The church also houses other works of interest, such as the wooden Romanesque sculpture of the Virgin of Casterillo.