The extension to the Faculty of Pharmacy in Madrid's University City lies in a right angle between the old Pharmacy building and the School of Medicine. The plot had a very low designated building ratio, which forced the architects to bury most of the building underground. The programme was divided over two volumes. A two-storey block containing the classrooms hovers above a U-shaped volume housing the laboratories. Both blocks are organized around a patio which connects with the street level via a slope. Medicinal herbs are planted on this slope in a pixel pattern, a reference to the knowledge taught in this building. The façades of the floating volume are done in red coloured concrete except for the northern one which is glazed. The irregularly positioned steel columns which support the volume, suggestive of a forest of straight tree trunks, together with the reflected image of the poplars in front of the building generate a nice game of natural versus artificial.