This tradition has been challenged as attempts have been made to express other important aspects of the building, such as the heating and ventilating equipment, which can amount to a large part of the cost, and be difficult to hide away. At the Centre Georges Pompidou in Paris, for example, the various service ducts and circulation systems — stairways, escalators, and lifts — are made highly visible, threading their way through the structure of the building to give it its particular character (Figure 25). The structure here is handled ingeniously, so that the large columns are mostly hidden within the building, and the structure that is visible in the main façade is hardly more than a network of fine steel, which has the appearance of scaffolding. The building, when it is swarming with people, seems to be little more than a support for the activities in and around it, which is its point. This is architecture conceived as a ‘facility’ rather than a monument. It is a place where events are made to happen, rather than a determinedly beautiful self-sufficient form. People who look at it in photographs see it as an assembly of girders, reminiscent of an oil refinery, but people who have visited it remember more clearly the journey up the escalator, the views from the top, which are extensive, and the rooftop café, the exhibitions, or the street performers. For such a large and colourful building, it is surprisingly reticent, but it works by such different means than does, say, the Parthenon, that we might wonder whether the same category, ‘architecture’, can be the right category for both of them.