This monastery is situated in Plaza de la Inmaculada and was founded by a group of Benedictines who, shortly after the discovery of the Apostle's remains, settled in the place called Pignario, near the Chapel of Corticela (now part of the Cathedral), where they held their services. The main developments took place after 1494, when it came under the Benedictine Congregation of Valladolid. Thereafter the wealth they accumulated enabled them to undertake the impressive construction of the church, which, along with the Cathedral, is the most valuable building of Galicia's baroque style. During 1991, after the monastic rooms were equipped and the valuable altarpieces were cleaned and restored, it housed the anthological exhibition of Galician art Galicia no tempo. In the year 2000, when Santiago was a European City of Culture, it housed the exhibition 'As Faces de Deus'.
The architects that worked on the church were the Portuguese Mateo López, who did the first designs; Bartolomé Fernández Lechuga from Granada, who built the magnificent ribbed dome and organized the interior, producing a space of great majesty; Peña y Toro from Salamanca, who did the containment work since the walls gave way and, finally, Fray Tomás Alonso and Fray Gabriel Casas, who made different contributions to the monastery façade, cloisters, belfry and monastic rooms. An attractive plateresque façade is displayed above the door. The central part, between the door and the oculus, is dominated by the Virgin, St. Benedict and St. Bernard, while the pediment crowning the front depicts St. Martin sharing his cape with a pauper. The towers only rise to the height of the façade, due to the opposition of the Cathedral's chapter, which was afraid that the view of the basilica would be blocked. In order to overcome the difference in ground level, the Benedictine Plácido Camiña built the beautiful stairway leading up to the door, which is undoubtedly inspired by the one leading to the Cathedral's Obradoiro façade. The church has a Latin-cross ground plan with three naves in its main arm and one transept nave, with a continuous balcony all around. Barrel vaults are employed in which the ribs are disguised as false coffers. There are several chapels, linked to each other, on each side of the longitudinal arm. An outstanding feature inside is the magnificent baroque high altarpiece designed by F. de Casas y Novoa and made by Romai. Closing the façades of the transept, there is the Altarpiece of St. Benedict in the north and the Altarpiece of the English Virgin in the south. In addition to the aforementioned ones, we can also contemplate the altarpiece in the Chapel of Socorro, the Altarpiece of St. Scholastica, the Altarpiece of the Christ of Patience and the Altarpiece of St. Gertrude. It is also worth highlighting the choir stalls, made in walnut by Mateo de Prado and considered the most important made in Galicia and among the most important in the Iberian Peninsula.
The monastery reflects a very simple and cold design, with the only exception of the façade, which is reached by means of a large stairway. The façade is divided into three parts with a central section bordered by two four-storey walls. The five-section tower helps to break the monotony of the façade. The doorway, framed by several Doric columns, houses an image of St. Benedict and is crowned by the structure added by Fernando de Casas, which includes the Spanish coat of arms among scallops and the figure of St. Martin of Tours. Within the monastery there is the cloister of offices, which is the oldest, and the processional cloister.