A new methodology for digital image processing, namely the Motion Magnification, allows to magnify small displacements of large structures. Motion magnification acts like a microscope for motion in video sequences, but affecting only some groups of pixels. The processed videos unveil motions hardly visible with the naked eye. We apply the motion magnification to a scale mockup of the Hagia Irene church stressed by a shaking table, to the so-called Temple of Minerva Medica in Rome and to the Ponte delle Torri of Spoleto. Results are surprising, offering a low-cost, viable support to the standard equipment such as contact accelerometers, laser vibrometers, linear variable differential transformers.