While there are lots of places you could potentially get this trophy, the best place to get it is actually the first Location of the Mastery Challenges DLC and in Particluar the Raven Challenge there, to Get the Gold you Need to Remain Undetected Assassinate 13 Enemies and Steal 4 Artifacts.
So you don't even need to Get the Gold Medal you just need to make sure you kill 10 of the enemies in a row without getting spotted.
If you do go for Gold you'll get this DLC trophy