Load up the Wayne Manor predator challenge. You can't use any gadgets or take any damage. No grapnel, nor anything on the d-pad. Detective mode is OK. Should your life bar appear in the top left corner, you've been hit and should restart.
There are six enemies on this map including a gatling gun enemy. There isn't too much to this one, Keep detective vision on at all times and use silent takedowns, leaving the gattling gun enemy until last.
For me, I went to the right almost immediately and took out the guy by the piano. Using those stairs I went upstairs and took out another enemy. At that point, the bodies were being discovered. Using the stairs became less stealthy; so I used the vent in the main lobby towards the back, once in there, you can access a ladder to get upstairs as well. From there on out, it was just a matter of doing silent takedowns on the other three regular enemies, then doing a beat down on the gattling gun guy. Remember, once you start the beat down on him, you will have to watch out for instances when you need to counter.
For those of you who prefer a video, see below. All credit to the original poster.