The latest Mars orbiter has a high density image camera which is beginning to take pictures of the entire planet at a resolution never before possible. (Objects the size of cars can be clearly seen.) Here's one out of some of the early batches, taken last week.
Link to photo at NASA/ JPL.
They're tentatively calling it a "crater" but come on now. At that resolution, it sure looks like the corner of the foundation of a building, crumbling and ancient, but still... how many craters create structures with 90 degree angles???
I mean, sure.... just like the "Face on Mars" pictures, light can play tricks and this could turn out to be something completely normal, but still... makes you wonder, doesnt' it?