Riddler's revenge is one of the side missions. This is the most complex side mission of all available in the game, because here, you need to complete then trials of the Riddler. Additionally, to end this mission, you also need to find and solve all the 243 puzzles thought up by the criminal.
It is impossible to miss this mission. What is even more, during the main storyline of the game, the premises of this mission, and the troublesome situation that the Catwoman has gotten herself into, will be communicated to you. To learn more, see Find Catwoman at the Riddler's Orphanage, in the walkthrough for the game's main storyline. After you have unlocked this side mission, you can head towards the track line in Cauldron, where you need to solve the first Riddler trail. Make sure that you are driving the batmobile, drive into the garage and wait for the elevator to start.