Many architects use optical illusions to appeal to those viewing the structures. Mostly the illusions are used as perspective illusions, to create a feeling of largeness, even if the structure is small. The most common way this is done is by making the structure get narrower as it goes away from the viewer. Other optical illusions are made just for the enjoyment of the person, by making structures seem abnormal. Another common structure that is almost always an optical illusion is a movie set, where things can seem bigger than they really are from the camera's viewpoint.
http://weburbanist.com/wp-content/uploads/2012/02/regina-silveira-1.jpg
http://www.illusionking.com/illusions/architectural-illusion-1.jpg
http://img.weburbanist.com/wp-content/uploads/2008/11/optic_illusions_4.jpg
http://freshbump.com/thom-faulder-s-tree-of-optical-illusions/
http://images.freshnessmag.com/wp-content/uploads//2011/11/macquarie-ropemaker-place-hq-clive-wilkinson-architects-00.jpg
http://artinspired.pbworks.com/w/page/13819516/f/awesome_optical_illusions_main1.jpg
http://www.free-jokes-online.com/thumb/optical_illusion-bus-stand.jpg
http://www.illusionking.com/illusions/architectural-illusion-1.jpg
http://img.weburbanist.com/wp-content/uploads/2008/11/optic_illusions_4.jpg
http://freshbump.com/thom-faulder-s-tree-of-optical-illusions/
http://images.freshnessmag.com/wp-content/uploads//2011/11/macquarie-ropemaker-place-hq-clive-wilkinson-architects-00.jpg
http://artinspired.pbworks.com/w/page/13819516/f/awesome_optical_illusions_main1.jpg
http://www.free-jokes-online.com/thumb/optical_illusion-bus-stand.jpg