This is for beating the fifth riddler challenge which is only available after beating the fourth.
Head to the waypoint with the Batmobile and enter the garage. You must have opened the bridge to let the batmobile on the island to progress with this one.
This is a simple challenge.
Get in the batmobile, and note the pressure pad vertically on the wall in front of you. It's impossible to stand on, but....
Take a run up and eject from the batmobile and glide into the pad. This unlocks a gate behind you.
Return to the batmobile, and eject glide again. This time glide forwards, do a 180% turn and hit the pad now in front. The gate to the tunnel is now open.
Same again....glide towards the second pad, but glide through the tunnel just to the right of the pad. Take a hard right at the end, then glide into the pad in front of you.
Once all three pads are hit, use your batarang on the now illuminated '?'.
Go stand on the pressure plate and locate the correct key position. Switch to catwoman and collect the key for your achievement.