We can actually "look" at the bulk shape of crystals which often reflect the internal shape of the tiny constituent particles. In the case of naturally found gold crystals, they form an octahedral shape and this would suggest that the underlying gold atoms have an octahedral geometry. See Figure 16 in this picture of such a naturally found gold crystal: https://vixra.org/pdf/1303.0184v1.pdf

This paper also explains why you might expect that any large atom takes on an octahedral shape. If you were to invent a sufficiently powerful optical microscope and you could look at a single atom, this paper shows what they might actually look like.