Solved in Arkham Knight HQ South ... When you leave the fan chamber, you'll spot a Riddler puzzle on the other side of a gate. To reach it, look for a vent just over the nearby alcove.

"The League of Assassins stuck blades through hearts, now they impale each other's art." There's a large ... go into the tunnels to search for the Arkham Knight, look for this on a ledge when ...