The museum's collections are multidisciplinary, classified into rooms for painting, sculpture, archaeology, decorative arts, engraving and ethnography.

The different rooms traditionally displayed archaeological collections, pre-Roman and Roman goldsmithery, silverware and Gothic, Renaissance, still life and Spanish paintings.

Three rooms in the Castro Monteagudo building are dedicated to archaeology, presenting significant remains from the prehistoric and protohistoric stages of Galicia.

The collection of civil and religious silverware, on permanent display in the Castro Monteagudo building, was acquired by the writer and diplomat Gonzalo Fernández de la Mora y Mon.

The most valuable piece is an imperial tureen, forged in Strasbourg in the 1800s, as well as a trophy jar given by the Empress of Germany, Augusta-Victoria of Schleswig-Holstein-Sonderburg-Augustenburg, to the winner of a race in 1898, with gold coins inlaid with the effigies of the three emperors who ruled in the same year.

The collection on display in its rooms includes furniture and navigation equipment, the cabin of the armored frigate Numancia, religious sculptures, pottery and a traditional Galician cuisine, Engravings, Sargadelos earthenware and jet objects.

It exhibits a large collection of romantic and historical paintings from the 19th and 20th centuries, with rooms specifically dedicated to Goya and Joaquín Sorolla.

In 2007, its collection included over 6,000 serial titles, over 150,000 bibliographic records, 500 maps and plans and documentation sections.

It occupies the remains of the convent of San Domingo, built in the 14th and 15th centuries and abandoned after the Spanish confiscation of Mendizábal in 1834.

In addition to the remains of the church itself, which are still standing, the ruins also contain a large collection of coats of arms, tombstones, canopies, Visigothic and Romanesque capitals and various Statues.

The collection of Torcs and other pieces of the Castro culture from the treasures of Caldas de Reis and Agolada, among others, is particularly noteworthy.

The first floor is dedicated to Galician art, from the Gothic period to the end of the 19th century, under the name Xeración Doente.

Sculptures and relics are on display, including the altarpiece of Santa Maria de Belvis (from the Dominican convent in Santiago de Compostela), and various paintings and sculptures by Goya, Gregorio Fernández, Xosé Gambino, Jenaro Pérez Villaamil, Serafin Avendaño etc.

Works by Ovidio Murguía, Álvarez de Sotomayor, Camilo Díaz, Asorey and busts and instruments by the violinist Manuel Quiroga Losada can be seen here.

Dating back almost 100 years, Anderson's pictures and the recreated scenes of rural life showed, among others, milkmaids gathered in Santiago de Compostela's Rúa Nova at dawn, women carrying ceramic pots to market, craftsmen selling wooden clogs and people in traditional raincoats made of straw.