Go to Vegas
I'm not sure if this true in the real world, but I've read a couple of stories in which Las Vegas hotel/casinos will change gold ininto chips for a slight premium and with few questions asked. The idea being to cater to people from other countries that might not have legal tender, or have some other reason to use gold instead of some other form of currency.
Go to Vegas, change your gold, looselose some money at the casino so they are happy, then cash out your new riches and go home.