For the five-storey extension, white marble rather than black basalt was mixed with the river gravel from the nearby Rhine Valley in creating the concrete. Here, too, the final layer of the material was smoothed and polished, which makes the stones glint in the sunshine. Depending on the incidence of light, the facade reflects the surroundings with varying colours and lighting intensities.
An unusual feature of the building is its inner organization. The jewellery shop and the Hilti Art Foundation occupy the lower ground floor, while on the floors above, the functions alternate. Circulation in the two realms is completely separate, which explains the two staircases in the plans. Curved stairs in the foyer of the museum of art lead visitors down to the first exhibition gallery in the new structure, from where they have access to a staircase space some 20 metres high. Seemingly endless staircases without landings rise over two storeys, to where the 50 currently exhibited objects – from a collection containing some 200 works – are on display.
