This "hole in Mars," imaged by the Mars Reconnaissance Orbiter, is an opening into an underground cave. The hole is approximately 35 meters across. NASA reports, "Holes such as this are of particular interest because their interior caves are relatively protected from the harsh surface of Mars, making them relatively good candidates to contain Martian life."
David Pescovitz is Boing Boing's co-editor/managing partner. He's also a research director at Institute for the Future. On Instagram, he's @pesco.