A glass box is contained within the one-metre-thick walls that follow the contours of a former cloister garden and are built of the same sandstone as the neighbouring cathedral. ­Only a few openings link the hortus conclusus to its surroundings. The dematerialised impression of the box is achieved through the double skin of laminated safety glass. There are no profiles disturbing the minimalist design, which includes silicone joints between the glass panes and lower guide-rails recessed in the ground. On the upper level, glass fins between the panes of glass stiffen the structure. They seem to disappear in the edges of the floor decks, where an intricate system of steel profiles connects the glazing to the solid core.