Walls are practically very normal.
In fact, art should always be that normal,
and always just art...

Has it ever occured to you that walls always have a function? Constructive, defensive, rejective, and so on. These might be literal or metaphorical, but they always have a function. The walls of a residence have a constructive and supporting function. The walls of a fortress are (or were) also defensive. Metaphorically, you could think of ‘erecting a wall’ or a ‘wall of water’.
Of course, the first wall that comes to ones mind is The Wall in Berlin. But if you think about it, many walls are passing by, for example in music or the news. Remember Pink Floyd’s record The Wall. Also, we all know the Chinese Wall. Another wall, which has been in the news more recently, is situated in Israël. This will probably sound familiar to you. Did you know there are also plants called Wall? Pimpernel for example, is in the Netherlands also known under the name ‘Red Wall’.
Let’s go back to the ‘normal’ walls now. Everybody knows them: sometimes they bother you, when you need to hammer a nail into a rock-hard wall, sometimes they are useful, because they allow you to hang photographs, but most of the times, they are just there, without many people really thinking about them.

By the pictures of the old factory walls, different thoughts and emotions are aroused. At least, there should be! Some pictures almost allow you to hear the shuffling feet of passing workmen, all worn-out by a long day of heavy work around noisy machines in badly lit and ventilated rooms. You can almost see these people waste away.
Try to imagine how much love and craftsmanship was used to build those walls, brick by brick. Now, after many, many years of hard work, these walls also show signs of wear, caused by the ravages of time.
You don’t know anything about the building we are talking about, it’s just knowing how to look at a (once beautiful, new) wall. In the meanwhile, give your imagination free rein.