A ball-and-stick chemical model of gold, made out of gold, that fills most of a 50x50x50 underground vault and is heated by magma pouring in from the top. Furniture is all gold or artifact, and the rooms were intended for royalty (but then it turned out that my civilization has no royalty). This save file contains a fortress with a small, poorly constructed, but totally awesome megaproject.

Go to hotspot 4 for the bottom of the structure.