batman arkham asylum how to do riddle when the door is locked after harley quin leaves?

[Mr Ballsdrop]

When you go in a room harley quin is behind a glass pain. You have to free guards from the ropes, but without electricuting them. But when you've completed that part. You go out of the room the door appears to be locked. So how do you get back into the room if you missed the riddles. (there must be a secret tunnel or something). I need a good description for an answer please.

[Weemanbiggy]

Once you've finished the game you can go back and get any riddles you might have missed, you can get back in there (grapple up in the room with the two guards in it) but as it's filled with gas and at that point you don't have the necessary upgrades to get rid of it there's no point.

[cool dude]

Please give riddle and In the meantime use detective vision everywhere