The first impression of the Federal Building, which is in the South of Market district, is somewhat intimidating. Its inscrutable facade is shrouded in a perforated-stainless-steel scrim, which is mysteriously sliced and peeled away, apparently at random. At the base of the building, the screen mutates into a folded roof that covers what appears to be a greenhouse but is actually a day care center. The imposing pavilion in the foreground, whose complicated roof resembles a trestle bridge, turns out to be a coffee shop. As often happens in a Mayne design, many things are not what they seem.