*Solution by UnTaMeD x SaGe for the Win 8 version of this game*
This is straight forward, just start a Crossroads game and start playing through defeating monsters and collecting their coins.
This doesn't mean that you have to have 100 coins on you, all you have to do is collect 100 coins.
This means you are able to die to drop all of your coins and then pick them up again, which will count towards the achievement also.