Mars has hidden depths hinted at by intriguing pits scattered around the planet. Some of these tantalizing windows may be entrances to underground caverns. If humans ever make it to Mars, they may want to consider hunkering down underground to protect themselves from space radiation.
This image from NASA’s Mars Reconnaissance Orbiter (MRO) in 2011 shows a hole on the slopes of the Pavonis Mons volcano. “Why there is a circular crater surrounding this hole remains a topic of speculation, as is the full extent of the underlying cavern,” NASA said in an image feature in 2020.
This photo is stunning and fires up the imagination to excellent levels. A favorite since it was new.