The new building complements the existing museum complex – a former Dominican monastery dating from the 16th century with an annex erected in the 1930s. The extension contains a new entrance lobby, a hall for various events, an exhibition space, a cafe and a library. This narrow, 150-metre-long volume was inserted in the tight residual area between the monastery and the hillside. The rock face was removed in part, and the outer wall functions as a retaining wall. In contrast to the sandstone facades of the existing buildings, the front face of the new structure consists of a homogeneous clip-on skin of perforated cast-aluminium panels that unites the various functions and visually reduces the overall volume. The skin is partly overgrown, with mosses and ferns that thrive on Monte Urgull sprouting from the openings. Over the areas of glazing, the perforated panels function as a light filter, while affording glimpses of the plaza from the interior. At night, the building radiates light from within, hinting at the spatial complexity. Drawn close to the existing structure, the extension is then set back to create internal courtyards. At the northern end, an external staircase leads to the hill.
Parallel to creating the extension, the architects undertook the restoration of the existing buildings. Internally, therefore, the ensemble is distinguished by a uniform use of materials and textures, which provide a restrained background for the rich collection of objects from the history of the Basque Country. In addition to the dark iroko of the floors and stairs, the exposed concrete surfaces in the new structure are striking for the fine gain of the boarded formwork that was used.
The architects developed their “green wall” in collaboration with artists Leopoldo Ferrán and Agustina Otero. The planted facade, which may be seen as an extension of the environment transformed by art, consists of perfo-rated cast-aluminium panels fixed to a steel framework. The cavity between the panels and the concrete wall serves as a main-tenance space. Quilted mats with soil and gratings were fixed to the inside face of the panels for the planted areas. The vegetation grows through the openings. Watering and fertilization is computer controlled. Selected in accordance with the location and degree of exposure to sunlight, the plants reflect the vegetation on the slope to the rear.
