If you guessed Abraham Lincoln's eyeball, you are correct. You can hike up very close underneath Mount Rushmore and take pictures from a different point of view, one that brings out the detail in this enourmous sculpture.
I find the importance of a "catch light" in the eyes translates to all forms of art. The artist here took great pains to carve out the eyes in a way that left a block of white granite to create the illusion of a reflected light that makes eyes come alive, a very important feature to consider in portrait or animal photography.
It wasn't quite the right time of day to get that Rembrandt lighting portrait photographers strive for. They all have racoon eyes or look like they are wearing masks. Next time.
Mount Rushmore is a US National Memorial in South Dakota. It is worth a visit along with many natural and man-made curiosities in that area of the country.