Percival Lowell mapped the straight lines he observed on the Martian surface, which he believed to be intentionally engineered canals.
Bridge on the Moon
Robert Dyrda
This image shows the region on the Moon in which John J. O'Neill reported seeing a gigantic natural bridge in 1953.
The Face on Mars
NASA
In the 1970s, the Viking mission took this image of a formation in the Cydonia region of Mars that resembled a human face.
...Or Is It?
NASA/JPL/Malin Space Science Systems
In 2001, the Mars Orbiter Camera acquired this high-resolution image of the same formation in Cydonia, which showed the "face" to actually be a highly eroded mesa that looks like a human face at certain times, due to shadows and lighting.
The Inca City
NASA/JPL/Malin Space Science Systems
In 1972 scientists on the Mariner 9 mission gave the informal name "Inca City" to this area of intersecting ridges in the south polar region of Mars.