“Las Arquerías” is a state-run architectural documentation centre in Madrid. It is located in the arcades of the Nuevos Ministerios. During the 1980s parts of the arcades were converted into an exhibition room by Alejandro de la Sota, but little of this now remains inside. This recent project provided a new lecture hall and underground vaulted exhibition room.Access to the new lecture hall is direct from the Paseo de la Castellana, through a heavy steel sliding door. This leads onto a gallery overlooking an impressive and very simply designed auditorium; this bright, high space, with good, largely glare-free illumination, was created by removing the vaulted ceiling of the underground level. A staircase leads down from the gallery, past a steel-framed projection and interpreting booth, to a basement with a U-shaped liner of exposed concrete. This solid concrete structure takes over?the job of cross-bracing the building from the former ceiling.