The chapel of La Piedad was built from 1530-1531 funded by Don Rodrigo Mercado de Zuazola.
The chapel can be entered through a 7 meters wide and 8 meters high grille and its central theme is a scene of Piety. On the side of the presbytery there is a second 3.85 meters wide and 8 meters high grille, very similar in its structure, ornamental richness and fretwork to the previous one. One may read the date 1535 on it.
In its interior, the north wall appears to be covered by the mausoleum of bishop Zuazola built with Filabres marble before 1532 and whose author seems to be Diego de Siloé, though there are no documents to support this authorship.
The mausoleum is ordered architecturally in the form of an altarpiece. In the central niche one may find the sculptural group of Don Rodrigo prayerful, assisted by a virtue and accompanied by a servant with a relief of the Holy Spirit between clouds and angels in the background
The altarpiece of the Piedad occupies the front of the chapel. It is of plateresque style and was built as per the existing documentation between 1533 and 1536. The sculptors residents of Oñate, Martín de Iragorri and Juan de Olazaren and Andrés de Mendiguren and Juan de Ayala participated in the work. It comprises of a seat, three bodies and an upper part, in five columns, all in relief.
In front of the mausoleum is the tomb of Don Rodrigo, in chage of Pierres Picart. It stands out due to its simplicity with the altarpiece and the mausoleum, as it only consists of a sarcophagus sustained by a quadrangular pillar with base and plinth and three cherubs in the capitals. One may read the date 1548 on a signboard.