At the end of the corridor there is a light beam from a video projector, with a mirror behind it, but there is no projected image in any surface.
The image is adrift until it encounters with viewer. As the viewer approaches the light, he/she sees the image projected on himself/herself through the mirror reflection. The invisible image becomes visible on the viewer’s own body. 
The image depicts  a shade of phantom-like figure making gestures and waving its hand in a background full of glares resembling either waves ou flames.