Citing evidence from Saturn mission photographs, self-styled astronomer Richard C. Hoaland proposes the radical theory that Saturn's moon Iapetus "is actually a 900-mile-wide, manufactured, ancient world-sized spaceship created under 1/40th terrestrial gravity according to a fractally apparent, 'tetrahedral' pattern!"
Without getting wrapped up in the potential tallness of this tale, take a look at some of the evidence that Hoagland seems to think confirms this hypothesis. A brief summary of the narrative with links to images taken from his six-part "Moon With A View" website goes like this:
Cassini, an unmanned Saturn-bound spacecraft validates images from the 1980's NASA Voyager mission that shows Iapetus' yin-yang, light-dark pattern to be the result of its asymmetrical spheroid shape. This is a geologic and gravitational anomaly. Based on its location, size, and density, it should be a perfectly shaped sphere, like our moon. But it isn't...
Several strange geological features were discovered on Iapetus, the first being a sixty-thousand-foot-high, sixty-thousand-foot-wide, four million-foot-long "wall"...spanning an entire planetary hemisphere...located in the precise plane of its equator!" also uncovered were rectangular, geometric, multi-storied, box-like buildings, shown here, as well as a "tower-like structure rising more than a mile above the surrounding terrain," not to mention evidence suggesting that Iapetus may be a perfectly constructed geodesic moon.
The remainder of the article continues to elaborate on the highly complex ways in which images of Iapetus have been taken and subsequently put together and studied by Hoagland and others to make this extraordinary claim. He also elucidates, in excruciating detail, several potential astro-physical and technological theories, linking Einstein, the discovery of DNA, and the origin of life on Earth to this controversial moon-craft.
Whether or not Saturn's Iapetus is telling evidence of intelligent extraterrestrial life, the images and possibilities that transpire from them are truly fascinating. Several scientists have debunked much of what Hoagland reports (which should come as no surprise). Dissenters can be read here and here, although it should be noted that the majority of this literature focuses on discrediting Hoagland's claims regarding conspicuous activity on Mars and not about the claims referring to the artificiality of Iapetus. An abundance of other alien-esque, conspiratorial information can be unearthed at Hoagland's website, Enterprise Mission.