The Casa de Convalescència was built between 1922 and 1930 within the boundaries of the Hospital de la Santa Creu i Sant Pau complex, in the Guinardó neighbourhood (Horta-Guinardó district, Barcelona). 

Barcelona's Hospital de la Santa Creu dates back to the 15th Century, when the city's cathedral chapter and the Consell de Cent governmental institution commissioned the building of a hospital in the Raval district to merge the five existing hospitals of medieval origin. The first stone was laid in 1401 but the building continued to grow until the 18th Century.

In 1622 arose the idea of creating a building devoted to convalescent patients, allowing these to be separated from patients with more serious or infectious illnesses. This project eventually got under way in 1629, thanks to an initial financial legacy. Work came to a halt in 1638 due to a fire, and resumed in 1646 thanks to a generous legacy from the merchant Pau Ferran. The Casa de Convalescència was administered separately from the hospital, having its own funds and patronage.

At the beginning of the 20th Century, Barcelona's overpopulation and the insufficient capacity of the Hospital de la Santa Creu created a need for a new hospital, on which work began in 1902, far away from the overcrowded Raval district. The chosen location was Guinardó, an area made up at that time of crop fields, pastures and scattered farmhouses.

The leading patron was the banker Pau Gil i Serra (1816-1896), who left a large amount of money in his will for the purchase of land and the construction of a civil hospital, which would incorporate the best medical, technological and structural features of foreign hospitals and would bear his name: Hospital de Sant Pau. In 1913, the hospital was renamed Hospital de la Santa Creu i Sant Pau.

The hospital complex was designed by Lluís Domènech i Montaner (1850–1923), a renowned Catalan‑Modernist architect and a contemporary of Antoni Gaudí (1852‑1926) and Josep Puig i Cadafalch (1867–1956). On his death, his son and collaborator, Pere Domènech i Roura (1881–1962) took over the project and it was he who completed the new Casa de Convalescència: a majestic building, located on the north-east corner of the complex, and opposite the hospital's Administration Pavilion, which sets up a dialogue between the two.

The building's façades are grandiose, theatrical and robust. The front combines the sobriety of its materials – brick and stone – with the sophistication of its medieval- and Renaissance-style decoration: blind arcades, semi-circular and stilted arches, trefoil windows, small rose windows, pinnacles, columns with floral capitals, watchtowers, running balconies and niches on the corners. It also includes a portico covered by a balcony that runs along the whole façade.

The Casa de Convalescència of Hospital de la Santa Creu i de Sant Pau had the same administration and the same functions as the old Barcelona Casa de Convalescència that had been built in the Raval district as from 1629.

Its costs were not met from the money bequeathed by Pau Gil in his will, as in the case of much of the hospital, but rather from the proceeds of selling the old Casa de Convalescència (1,750,000 pesetas) in 1925, and from private sources (masses and duties levied).

The building could house around 100 inmates, who could thus be kept away from the severely ill and the focuses of infection in the hospital itself. It was administered by the Sisters Hospitaller religious order, who also tended to the sick in the hospital, and it had its own chapel, chemist's, kitchen and refectories.

The vestibule is in the centre of the building and leads into the public and service areas of the ground floor (refectories, office and boardroom), as well as giving access to the first floor via the stairway. Its ceiling is covered by a sail, or handkerchief, vault and it has limestone columns with composite capitals.

The walls of the vestibule were decorated with historiated mosaics. On these, in 1923, Domènech i Montaner declared his intention to depict four scenes from the history of the Casa de Convalescència between the 17th and the 18th centuries, but the iconography was later to vary: the first panel was devoted to Elena Soler, a member of the Barcelona nobility, who had favoured the Casa de Convalescència in her will in 1656; the second depicted benefactor Lucrècia Gualba in 1629; and a third one featured the administrators of the Hospital de la Santa Creu on 24 January, 1680, when the old Casa de Convalescència received its blessing. In the 90s restoration, it was decided not to intervene in the mosaic fragments that had recently been vandalised, and which we know from photographs.

The ceramics, together with the glazed brickwork, not only had ornamental value but were easier to clean, provided better thermal insulation and stood up better to wear in high-traffic areas. For these reasons, they were used in the vestibule, the stairs, the offices, the refectory, the board room, the bedrooms, the secondary staircases – which have simple monochromatic ceramics – and in the garden porticoes, which feature Cartabón, or sail, ceramics, consisting of square tiles divided diagonally, and painted green and white, which were very popular in Catalonia, Valencia and Majorca in the 16th Century.

The main staircase, which is in the best state of conservation of all the building's interior areas, led to the chapel and the terraces. It is an imperial style staircase, consisting of a straight flight up to the landing, where it divides into two narrower, parallel flights. Another example, close at hand, is in the current seat of the Consell de Mallorca, the Majorca government, while further afield we can find others at the Winter Palace in Saint Petersburg and the Art History Museum in Vienna.

The walls are coated with Baroque-style ceramics, mainly in blue, green and yellow, which are based both on those of the old 17th Century Casa de Convalescència (now home to the Institute for Catalan Studies) and on contemporary models in the style of Seville's Plaza de España: pièce de résistance of the 1929 Ibero-American Exhibition. They are attributed in the literature to the painter and draughtsman Francesc Labarta i Planas (1883–1963), a member of Domènech i Montaner's team.

Moving from the bottom upward, we can classify the subject matter of the mosaics in five categories:

• Messages promoting Christian virtues, inscribed on Italianate coats of arms. From the Middle Ages onwards, hospitals were founded mainly on the initiative of the Church, which thus fulfilled two fundamental precepts of Christian doctrine: charity ("Thou shalt love thy neighbour as thyself", Matthew, 22, 39) and hospitality.
• The coats of arms of Barcelona, of Hospital de Sant Pau and of the Casa de Convalescència. The latter includes the arms of Hospital de la Santa Creu and those of the four benefactors of the old Casa de Convalescència.
• The heraldic coats of arms of the members of the Barcelona nobility who, in the 17th Century, funded the first Casa de Convalescència in Barcelona. From left to right: Elena Soler, Lucrècia de Gualba, Pau Ferran and Victòria Astor. The greatest contribution came from Pau Ferran, whose coat of arms, with its horseshoes, is to be seen all over the building.
• The building's inauguration date, in Roman numerals:  MCMXXX. King Alfonso XIII inaugurated the last pavilions to be built in the precincts during his visit to Barcelona in January 1930.
• Ornamental ceramics, combined with mouldings, to fill the empty spaces between the main panels.  These include elements and compositions of Catalan Baroque ceramics, many in the form of grotesques, with plant motifs, birds, vases, flowers, fruits, shells and cherubs. It is interesting to note that the ceramicist worked with older models in mind and copied motifs from the ceramics made by Llorenç Passoles for the old Casa de Convalescència in the 17th Century.

The main rooms on the first floor were the chapel – today the great lecture hall – in the middle of the building and, one on each side, the women's dormitories (to the north) and the men's dormitories (to the south), which were accessed separately by staircases placed at each end of the building. The first‑floor dormitories gave direct access to the balconies and terraces through French doors and windows. The second‑floor dormitories had no outside exits.

The building's perfect East-West alignment was ideal for exploiting natural light to the maximum, with its rooms and terraces enjoying the full benefits of sunshine and ventilation. Domènech i Montaner, following in the footsteps of Ildefons Cerdà (1815‑1876), adopted hygiene measures to improve the living conditions of citizens and patients.

The following can be seen from the top of the stairway, on the first floor:

• The chapel entrance, with its Neo-Baroque decoration and the coat of arms of Pau Ferran, the principal benefactor of the old Casa de Convalescència. The surname Ferran, deriving from the word "ferro" (iron), was represented on the emblem by three horseshoes, each with six holes. This coat of arms appears in different forms all over the building: on floors, lintels, capitals, stained-glass windows, mosaic panels, and more.
• A glass balcony surrounding the staircase, with Alfonso XIII-style woodwork and glass panes with ornamental motifs, including, from left to right, the coats of arms of Lucrècia Gualba, Pau Ferran, the city of Barcelona, the Carmelites and Elena Soler. Originally, the windows were close up to the staircase, and movement around the staircase was done from the outside, under a porch.
• The metallic staircase made of weathering (or Corten) steel. Proposed during the restoration of the building carried out by Tusquets, Díaz & Associates between 1995 and 2000, it improves access to the upper floors and facilitates the building's new functions. The office of the architect Òscar Tusquets was responsible too for restoring the Palau de la Música Catalana, also by Domènech i Montaner.
• The hospital pavilions closest to the Casa de Convalescència: on the left, the Saint Victoria Pavilion and, beyond this, the hospital's Central Pavilion: residence and workplace of the community of Sisters Hospitaller, who ran the hospital.

As we exit the Casa de Convalescència from this level, we can appreciate the rear façade of the building, which offers a remarkable interplay of volumes, achieved through the combination of openings of differing sizes and shapes, the pinnacles, and three types of domes: the principal dome, which is hemispherical, the four domes surrounding this, which are pointed, and the one that covers the stairwell, which is a flat dome on pendentives. Seen as a whole, the mix has a Turkish feel to it, bringing to mind structures like the old basilica of Saint Sophia or the Ortaköy Mosque in Istanbul, which Domènech i Roura knew well, as his own sketches show.

In one of the initial drawings for the project, a monumental fence was placed behind the building, together with a great avenue that would connect the Casa de Convalescència to the buildings beyond it.

The Casa de Convalescència had its own chapel, dedicated to Saint George. This had a height of 27 metres and was in the centre of the building, between the women's and men's dormitories. It was practically square in shape and was divided into three naves, separated from each other by columns with limestone shafts and composite capitals of Vilaseca stone. Halfway up, the chapel had long balconies, decorated with stone vases, from where patients who slept on the second floor could attend the services held there.

The upper half of the chapel featured numerous stained-glass windows – in the walls and in the drum of the dome – with heraldic iconography: the fleur de lis, and the arms of Pau Ferran, of Barcelona's cathedral chapter, and of Catalonia. They were made by stained-glass manufacturers Granell and Company.

The chapel's altarpiece was in the Neo-Baroque style, made of stone and alabaster, with small Solomonic columns of coloured marble and the image of Saint George. The stone part, at least, seems to have been carried out by a certain Mr Bartolí in 1928. Domènech i Montaner intended to commission a painting for the main altar that could compete with the notable work by Catalan painter Antoni Viladomat (1678-1755) that hung in the chapel of the old Casa de Convalescència. Most probably, new instructions and a lack of money led to a more modest solution.

The chunky, Baroquish features of the decorations in relief – on the lintel of the door and the cornices – are reminiscent of decorations in other buildings, such as the headquarters of the Spanish national telephone company in Madrid, designed by Ignacio de Cárdenas Pastor between 1926 and 1929.

Like the other grand areas of the building, for the purposes of hygiene and decoration the chapel featured polychromatic ceramic tile wainscoting with plant motifs. The outside surface of the dome was covered in glazed ceramic conche tiles in yellow, black and red.