Polygonal ridge networks are found in numerous locations and geological contexts around Mars. The best-known example for these features is Angustus Labyrinthus near the South Pole. Discovered already in 1972 on Mariner 9 data, the structure exhibits a rectilinear pattern of ridges and internal polygons resembling Incan ruins and therefor it was informally named “Inca City”. The formation of these features is still discussed and ranges from lithified dunes to clastic dikes to magmatic dikes. Later data showed that the ridges trace the part of a large, 86 km in diameter circle, so researchers also supposed an exhumed impact basin structure. Deep faults, created by the impact filled up by rising lava. Later, the softer polar plains material around was eroded leaving back the harder ridges. Another hypothesis is that the ridges are linked to the neighboring Dorsa Argenta formation, which contains many ridge segments interpreted to be eskers, a glacial landform. The left part of the image shows the intriguing Angustus Labyrinthus feature.