I've been holding back on this one. It is the most disturbing anomaly in the solar system - the Cydonia Complex of Mars.

In the plain of Cydonia, in the Northern Hemisphere of Mars, at 40.75N by 9.46W, are a series of unusual structures. There are several five-sided pyramids that are of incredible size. There are strange mesas that resemble human, feline, and alien faces. The pyramids and face structures are arranged in the position of the constellation Pleides about 17,000 years ago. This may have been when they were constructed.

Face Monoliths:

Martian Pyramid:

All of the structures have been damaged by severe erosion, as would be expected on a planet that is sandblasted annually by dust storms.

One of these structures resembles a prehistoric human face. It is about two kilometers long by one kilometer wide. It has a protruding jaw, that when flipped upside-down, resembles the face of a typical grey alien as described in thousands of abduction reports:

Some people have speculated that this a symbol of possible human-alien interactions at a primitive time in human history. It may be a monument to a hybridization experiment that may have created modern humans. There are many, many interpretations of the Face on Mars.

I think it is a piece of artwork, sort of like an Escher painting. It was designed to show intelligent life in the distant future (us) that someone was there, and they were creative, artistic, intelligent creatures. I do not think it was made by anything actually indigenous to Mars, but rather by visitors. I realize that this is speculation, and we will not know until we send people there to study it.

It is interesting that the Giza Complex, in Egypt, resembles a later version of the Cydonia Complex. Giza has human-like structures (the Sphinx) and three pyramids that match the position of the constellation Orion about 10,500 BC.

The parallels between Cydonia and Giza are unmistakeable and difficult to dismiss. The Sphinx has a human face on a cat body, facing laterally so it can be seen by an observer on earth. The Cydonia Face has a human/alien face facing upward so it can be seen from an observer on earth.

The Sphinx is so old that it has been severely eroded by water. This is clear evidence that it was built at a time before the end of the last ice age (~10,000 BC), when Egypt experienced regular rainfall. People who casually dismiss the Cydonia Face as being "natural" should look at the similar levels of erosion on the Sphinx.

The construction of the three pyramids at Giza are ascribed to various pharoahs. However, there are no actual hieroglyphic records of their construction. The later pyramids, built by and written about by the ancient Egyptians, are inferior copies of the Pyramids of Giza. They have not held up as well and are not as symmetrical. It is illogical to expect that ancient Egyptians made perfect pyramids on their first three attempts and then suddenly lost the ability to make them. It is far more likely that humans were inspired by the original pyramids, whoever made them, and copied their design.

I think the Cydonia Complex is the most interesting place in the solar system. It may hold evidence not just of an alien civilization, but of the interactions of that species with humans tens of thousands of years ago. It is far more than just another weird shape on a distant body that may or may not be artificial. It is so blatantly artificial and deliberate that it demands investigation. We need to go there.