Select one of the challenge types ( Ranked Challenges, Campaigns or Custom Challenges). Select the character you wish to play as ( Batman, Catwoman, Robin or Nightwing). Select Riddler's Revenge from the Main Menu. To play one of the challenge maps included in the expansion packs: These areas are also indicated on the Batcomputer Map with a pink Catwoman marker. To do this, look for groups of cats lounging together: you can switch between the two characters at these points by clicking the Left Mouse button. Once you have completed the main story, you will be able to switch between playing as Catwoman and playing as Batman as you explore Arkham City.
You will encounter these as you play through the story. The four Catwoman missions are included in the main game. Select the Harley Quinn's Revenge DLC option from the Main Menu.