Sim Building is a project of hospital which simulates different type of space organization in a structure type "plan libre". It forms part of the dense context of the old town of Valence (Spain), by reactualizing the standard characters of the street (circulation in balcony, porch, horizontality...), as well as the vocabulary related to the light (direct and indirect, downward or ascending, direct or projected). Two entities of different importance are joined by a vertical circulation, which remains the only constraint in the function. The second plate is entirely external and is arranged in gymnasium. The various consultations of the doctors spread around the central well of light.