Date of sighting: February 2012
Location of sighting: Earth's Moon

I was looking over this Clementine Lunar photo (source below) and found a wall like building that was on the far left side of the photo. The shadows and the roof have 90 degree edges which really makes this building out of place and easy to spot.

Source: http://www.cmf.nrl.navy.mil/clementine/water/southpole.JPG

Internet site reference: http://scottcwaring.blogspot.com