Many large buildings have a high lobby – some of these reach the roof, which in that case is often transparent. Some edifices also have an indoor water curtain in the lobby, or water running down a decorative wall. A way to save the cost of pumping the water up for such a waterfall is to rely on rain. The roofs of high buildings are flat anyway, in order to direct water into internal drainpipes, as opposed to sending the water over the eaves of a slanting roof. If the pipe from the roof is made wide, transparent and put it in the middle of the lobby, then whenever it rains, a waterfall occurs in the pipe. This works best in rainy climates and will be especially spectacular in intense rain and with a single pipe receiving the water from the whole inward-slanted roof. The lobby may become noisy though with the sound of all that rushing water.