This achievement is tied to the seventh of the Riddler side-missions.
*** Spoiler - click to reveal *** After you have gotten the 6th key for Selina, Batman has to drive to a location on Founder's Island. Once you are there take your batmobile down the elevator. You will be in a circular room with a big hole, filled with water, in the middle. You ll see 3 spots at which you can use the grapple hook of your batmobile to grapple down. These are marked 1-3.
Start at mark 1 and go down with your car. Rotate the wall until you have the batsymbol underneath your car. This will move one of the green circles to a spot which you can then use to glide through. Do so and step on the button inside.
Now you can go to mark 2 and do basically the same thing. Rotate until the batsymbol is under your car and glide through the green circle.
Now comes the only tricky part: Before you go to mark 3, go to mark 1 again. This time go one level deeper and start rotating. when you have done this you can finally go to mark 3 and rotate on both available levels till you have the symbol under your car.
Glide through the final circle and step on the button. Before you go back again use your car remote to get rid of the sentry guns.
You can now go down and step on the button at the bottom of the hole. Switch over to Selina and take the correct key.
If you need further help refer to the video below:
(video credit: PowerPyx)