To earn this, you must simply find 5 Gold Chests. These are usually hidden away behind broken walls, walls with glyphs or just plain out of the way locations.
As long as you explore, you should have no issues getting this, you can replay a level to find chests (I'm not sure if you can replay a level and open a chest multiple times, if someone knows, please let me know), so if you get to the final level and don't have this, replay previous levels.