Chapter 4: Sentinel Barracks in Doom: The Dark Ages introduces challenges for the Slayer to complete. In order to get 100% completion of each level, make sure you complete the challenges as well ...

This leads to a cemetery full of demons. The Blue Keycard is around the corner of the rocky hill. Secret #2 (Gold x8 + Life Sigil): Jump down from the Blue Keycard ledge to unlock the Blue Door below.