Open the door in front of your starting position, following the corridor to the west, and then the south. On making the second corner, a tripwire is activated. Run back to the starting room. The eastern wall is now open (sector 515), allowing you to access the set of shotgun shells and the two rockets behind the northeastern bars. Ascend the stairs to the east to meet a sergeant and a chaingunner. The path to the south is leading to a supercharge.
Follow the instructions in secret #1, but do not turn south following the corridor. Open the door, descend the stairs. Push the candlelit wall to the north to reveal a cacodemon and a passageway (sector 112) outside leading to an area where you find a box of bullets, two clips, two sets of shells, and a green armor. Follow the blood floor to the east to find a rocket launcher that can be reached by pressing the lion switch to the east of its plinth. This also releases an ambush, coming from the the north of the rocket launcher. There you find two rocket boxes. Follow the valley counter-clockwise to discover more items, guarded by monsters, among two ammo/weapon dropping enemies (troopers on easy, sergeants on medium or chaingunners on hard skill levels). Overall there a three clips, two bullet boxes, four sets of shells, eight rockets, a rocket box, a stimpack, five health bonuses and a berserk pack to pick up. Push the lion switch to the south of the bars to return to the building you came from.
Pick up the rocket launcher in secret #2. The sector is rests on (sector 597) counts as a separate secret.
In the west of the yellow skull key is a panel with a demonic illustration, press it and it will lower slowly. Step inside the wallspace (sector 137) to find a medikit, two rockets and three armor bonuses.
Press the lion switch to the southeast of the blue skull key, dropping you in front of an imp's cage. Swing around 180 degrees and press the gargolye switch before the platform raises again. This opens a wall at the eastern end of the blue skull key hallway, revealing a chainsaw, four health bonuses, four armor bonuses, and two stimpacks, guarded by four demons (easy) or spectres (medium and hard skills) (sector 650). Enter the northern passage to return to the corridor leading to the yellow door.
Press the lion switch to the northeast of the blue skull key to lower the computer map inside secret #5. Grab it before the plinth (sector 658) rises again.
Through the blue door, a platform will lower unleashing a string of imps and hell knights, among other monsters. The western canvas (with a pentagram on it) on the southern wall can be opened to reveal a cacodemon and a passage (sector 608) outside. After killing the monsters there, a switch in the northwest corner will lower the megaarmor plinth. Approaching it opens a closet in the south, containing five demons, five health bonuses and two rockets.
Facing the exit chamber, the second canvas on the wall to the right can be pressed to reveal three rockets, two health bonuses, and three armor bonuses (sector 524).