This strange object, photographed during an Apollo mission, has been named "the castle" by Richard C. Hoagland of The Enterprise Mission. It seems to have a definite structure, like the remnant wall of some ancient building. The bottom looks as if it has rows of support columns, above which is a high spire. Whatever it is, it's much brighter than the surrounding landscape. Is it just a trick of light and shadow? A photographic anomaly? Or is it all that remains of some rich Martian's get-away retreat?
Compare it to the photo on this page of the World Trade Center rubble.