To find the gold, you'll need to read the interesting article about the Southern Hemisphere's only bridge with residential accommodation (but there really is gold under it!): ickshovel:
http://www.abc.net.au/news/2018-08-...iving-inside-the-walter-taylor-bridge/9986992
http://www.abc.net.au/news/2018-08-...iving-inside-the-walter-taylor-bridge/9986992