Natural or not. Punch this into Google Maps: -79.975453, -81.988942 and be sure to check out the accompanying images. If natural, it’s pretty cool, but if it is man-made that would be even better. It is located close enough to South America for people to have explored Antarctica thousands of years ago.
Natural pyramids do occur in nature, as is the case with the Walshs Pyramid in Australia below. The Antarctic pyramid is said to be a Nunatak, a peak that forms from a glacier pushing the crust up into a pointed hill, which is then shaped by erosion.