An annex became necessary fort he collection building, originally designed by Herzog & de Meuron (completed 1992, Basil, realised by J.P. Meier-Scupin), because of unexpectedly high number of visitors, an increasing collection and expanding functionality of the building. In order to not interfere with the architectural concept of the solitary building, the annex was ‘docked’ to the existing building underground.

The only daylight comes in on the opposite side, through a skylight that can be sealed off. The annex building was realised with cost efficient technical and electrical systems, e.g. wall tempering and ventilation through a geothermal exchanger. The annex was also ‘invisibly‘ integrated into the newly designed gardens. In 2004, the annex was designated to be used for media presentations.