In late 1999, while imaging areas near the south pole of Mars, the Mars Orbiter Camera spied this interesting and familiar formation. You might be forgiven thinking this is a pit or collapsed structure. In fact, it's a mesa, 250 meters across, raised above the ground!

This is due to a well-known illusion; our brains are used to seeing things lit from above, but in this image the heart is being lit from below, confusing our sense of depth. I took the image, flipped it over, and inset it on the lower right. Does that look more like a raised flat region to you?

Original release.

Image credit: NASA/JPL/Malin Space Science Systems