Find all "official" Secrets on PlayStation Doom level 58,
The Mansion:

There are 5 "official" Secret areas on this map that will
contribute to a players Secrets score.  (Some other hidden
areas/items on this map will not affect the score.)
To reach all 5 official Secrets, you'll need the blue
key and the red key.

Secret 1: From the starting room on the west side of the
map, unlock the blue door and step into the hallway that
leads east.
Walk east down this hallway and you'll begin passing by
green torches to your left and right.  The second torch on
your left is special: Activate it like a switch, and a
wall panel will open just to the right side of the torch.
Step through this opening, and down into a narrow, winding
stone tunnel to get credit for discovering a Secret.
To return directly to the hallway, simply go back and open
the south end of this tunnel, and step through.

Secret 2: Near the center of the level (close to Secret 1,
above) is a 4-way intersection: three ground-floor paths
come together in a red-carpeted T shape, and a fourth path
to the east is raised above ground level.
The southern-most path is very short and ends in a blank
wall.  Step up to this wall and Activate it like a switch,
and the wall lifts to reveal a small, very dark room with 3
vertical flashing red panels.  Step inside to get credit
for discovering a Secret.
From here, go back to the center of the 4-way intersection.

Secret 3: From the middle of the 4-way intersection (see
the description of Secret 2, above), step north into a
short section of corridor.  Turn left to face the blank
west-side wall of this corridor, and Activate it like a
switch.  It opens to reveal a wide, shallow secret chamber.
Step in to get credit for discovering a Secret.

Secret 4: From the starting room on the west side of the
map, go up the short curving stairway to reach the door
that's high up in the south wall, between a pair of wide
bookcases.
Go south through this door, and you'll step into a square
room with a large cage at the center.  Go around this cage,
and approach the south wall of this room.  In the middle of
the wall, a shallow stream of red ooze flows through a low
opening at floor level.  Activate the wall just above this
stream, and a section of the wall lifts to reveal a green
armor jacket at the far end of a short passage.  Pick it up
to get credit for discovering a Secret.

Secret 5: There is another chamber just beyond the small,
dark room mentioned in Secret 2, above.  In this chamber is
a secret-exit switch.  To access this final chamber and get
credit for discovering the Secret, read the walkthrough for
this map's secret exit.