The farther down one goes the more of these bridges there are until at a certain point the distinction between building and not-building becomes zero. Everything shares a common and irregular skeleton of steel. This is the level at which peculiarities start to become apparent. Interior walls here are often former exterior walls so tinted or reflective glass is quite common. There are many concrete ledges that sit at the edge of a room or occasionally serve as sidewalks, when they are wide enough. There are quite a few plazas containing skylights or air intakes that lead into rooms below. A few such plazas have ancient gargoyles guarding the perimeter. Certain roofs are steeply sloped and are unsuitable for occupancy so are instead surrounded by huge glass panels so their beauty can be admired. This is especially common when the roof in question is a dome or is covered with gold leaf. In one case the roof was enclosed and converted into a very splendid fountain which attracts many people every day. Many of the enclosed sloping roofs are shingled with blocks of slate or intricately carved clay tiles, though by a small majority the most common material is metal plates of steel, copper, or bronze. Practically all of the uppermost roofs of these levels are metallic and at certain times of the year sunlight penetrates the canopy of towers and reflects into public areas which were built in the appropriate places to take advantage of this effect. These places are very popular for weddings at such times. ascend descend