Build a City that is well surrounded by water or desert, (again 6+ tiles would be best) and fully develop it (Market and Bank is needed). Use a Great Personality that boosts Gold and put your City on Gold Production. Building The Internet and The Trade Fair of Troyes, (which are Wonders), will help you get this faster. You should be able to get it somewhere around City Level 25. Or if you done the Achievement above just use the same city (making sure said city has Library and University) and change to Technology Production.