After three years of work, the Unterlinden Museum in Colmar, France has re-opened to the public, with a new subterranean gallery space created by Swiss architects Herzog & de Meuron.

The museum – which exhibits historic works of art from the likes of Claude Monet and Pablo Picasso – has almost doubled its interior space by linking the museum with an adjacent complex of historical buildings, including a 13th century convent and the city’s historic municipal baths.

Architect Richard Duplat was responsible for renovating the convent, which houses the famous Isenheim Altarpiece – a sculpted piece of religious art created by German artist Matthias Grünewald in the 16th century.

The convent is linked via the tunnel to a new three-storey building created by Herzog & de Meuron, which was built using irregular hand-broken bricks to complement the facade of the older structures.

A huge concrete spiralling staircase links down to the tunnel, which which contains three exhibition halls.

“We sought an urban setting and an architectural language that integrates into the old town, while expressing its contemporary character,” said the architects in a statement. “The project needed three dimensions: an urban presence, architectural features and a focus on the museum itself.”

The museum’s inauguration ceremony was held by French president Francois Hollande, who called the museum “a place of pilgrimage for culture, beauty and emotion.” The cost of the project was €47m (US$52.7m, £36.4 m). Around half was provided by the city of Colmar, with the other half coming from the French state and the Alsace Region.

Herzog & de Meuron collaborated on the project with French practice DeA Architectes and structural engineering firm ARTELIA.