These two structures on Mars in some Spirit Rover photos. They were both in Sol 2087. The first one looks like it was once an opening to some kind of vent having two 90 degree angles. The second one is a curved structure with a square cut out of it (four 90 degree angles). Both anomalies must have been seen by NASA scientists, but I am sure they didn't plan on the public being so investigative on the subject.
