This chapter proposes the term "architectural ghosts" for human-made structures that no longer exist and can now be known only through traces that they have left—in memory, in landscape, and in photographs, drawings, and paintings. It argues that architectural ghosts deserve our aesthetic consideration and that a robust and complete conception of architectural appreciation has a place for the appreciation of architectural ghosts. Architectural ghosts, too, can arouse a variety of emotions. Architectural ghosts can arouse sadness. There is a continuum between architectural ghosts and ruins. Perhaps particularly haunting are the architectural ghosts that survived into the era of photography. The best-known architectural ghosts may be the twin towers of the World Trade Center in New York City, destroyed by terrorists in 2001. A place for the appreciation of architectural ghosts helps fulfill the desiderata and also allows consideration of the human past and the relevant moral issues that have shaped and continue to shape the built environment.