The construction of the interior space is the result of a set of design and construction operations. The first of them consists of sliding the formwork of the floor plans of the rooms, forming a set of polygons that regulate the different surfaces that make up the first interior façade. This set of plans that energise the space help to control the acoustics of the great hall. This first enclosure is built using concrete cornices and railings made in two planes, one of glass and the other of cast aluminum elements, which, while maintaining their diaphanous and crystalline quality, avoid the problems of vertigo, cleaning, maintenance and the replacement of its various parts. Two slots, one for lighting and the other for air injection that pressurises the corridors, complete this first membrane. This façade is complemented by the interior that encloses the rooms formed by the elliptical surfaces that enclose the bathrooms, covered with curved sheets of aulocobond and the cylindrical pillars lined with mahogany palm of equal section throughout their height, which they collect the tickets from the rooms. The second project operation is developed in the section. This space is structured vertically in three parts: the lower one, 10 m high, topped by inclined curved surfaces that correspond to the closure of the technical plants and which, due to its slightly vaulted condition, reinforces the personality of this first level which also has differentiated air conditioning. The second level, which is part of another visual plan, is made up of the twelve floors of rooms that make up the central part of the 42 m high space through the game of polygonal axis. Finally, the two floors recede allowing light to enter and smoke to escape, which would turn this space, in the event of a fire, into a zenithally open patio. The last floors with the curved layout and the opaque windowsills act as the end of this whole space. The lighting is achieved with a large stained-glass window facing north and is stiffened with broken and horizontal ribs. A set of metal profiles make the knots, and, in their folds, there is the structural metal carpentry that supports the glass. A canopy goes through the stained glass to collect the access and arrival of cars. This large stained-glass window and openings in the roofs illuminate the hall with northern light, making artificial light unnecessary. This causes the spatial perception to be reversed during the night or day. When it is daytime, the space is projected outwards, accentuating the natural light on the facets, edges and planes. At night the process is reversed, the space closes in on itself, the artificial light marks and follows the lines and the stained glass that reflects the interior and shows the emblematic lights of the city. On the sides of the stained glass are two large concrete screens made with sliding formwork and which contain all the vertical installations serving each floor for connecting and closing circuits. These walls include the air conditioning, extraction and renewal of air in the bathrooms, evacuation of gases and chimney ducts, trolley lifts, suitcase lifts and clothes ducts, the plant offices, emergency stairs and safety installation. These walls make the relationship between the users and all the service networks without crossings possible, and form the main access façade on the outside, depriving the view of the rooms from the outside and causing a strong change in scale which helps place the building on the ground.