Doom II has two secret levels designed as a tribute to other id titles. The first secret level titled "Wolfenstein" is largely based on the first map in Wolfenstein 3D. A secret exit in the level leads to the second secret map, titled "Grosse", referencing Hans Grosse, the first boss in Wolfenstein 3D. To beat "Grosse", the player has to shoot four hanging Commander Keens and flip a switch. Commander Keen is the protagonist in multiple platformer games also developed by id.