The sheer scope of the colony - 40 tons of soil displaced, to create a network of tunnels the size of a small house - is absolutely stunning. It's laid out in a coherent way - main arterials for ant traffic, side roads, regularly spaced chambers, and a frickin' ventilation system to get rid of carbon dioxide from their fungus gardens - and yet there was no single architect behind it, but rather the collective consensus of the colony.
Nature never ceases to astound me.