This is a triangular square that is popularly known as the "Crystal Square", referring to the minerals found in the region. It was designed by the artist Roberto Burle Marx, but was forgotten for nearly twenty years before being completely abandoned. In 2009, it was restored. Here you can see the headquatters of the army, and the Teatro Pedro Calmon with permanent exhibition on the history of the army (with old photos, materials, uniforms ...). To visit the barracks you have to organize the visit in advance. Hours: Monday to Friday from 9 to 17h.