Level 13: Dark Citadel: 2 Secrets

From your starting alcove, exit and turn left, proceeding straight until you hit a wall. Press C-Right against the wall to reveal a secret area. Inside, you will find Rockets, a Backpack, an Energy Cell Pack, Boxes of Bullets, and Shotgun Shells.

After finding the first secret, continue through the level until the door near the starting point opens. Go through this door and take the left path. In the next room, enter the opening in the corner. In the small hallway, examine the left walls until a hidden door opens. Enter this room for the second secret. This area contains two hallways; one leads to a Megasphere and the other to a BFG.