How to get the red key in PSX Doom level 58, The Mansion:

Background: In the southeast corner of the map is a
rectangular courtyard.  At the east end of the courtyard is
the red key, sitting on a short pedestal in the middle of a
small "field" of teleporter pads.  The red key can only be
acquired by navigating a winding path through the
teleporters.

Look on your Automap.  The field of teleporters surrounding
the red key appears as a 5x5 "grid" on the Automap:

[_][_][_][_][_]
[_][_][_][_][_]
[_][_][#][_][_]
[_][_][_][_][_]
[_][_][_][_][_]
-----------------------------------------------------------
Notes: "[_]" represents 1 "square" of the teleporter field
("grid") as it appears on the Automap.  "#" represents the
pedestal where the red skull key sits.

Approach the grid from the west side, and step on each
square in the alphabetical order indicated below, starting
with square "A":

[_][_][_][_][_]
[A][_][K][J][I]
[B][C][#][_][H]
[_][D][E][F][G]
[_][_][_][_][_]

Once you get to "K", turn south to face a switch on the
central pedestal.  Activate it and the pedestal lowers,
granting you access to the key.

Note that stepping on any square other than squares "A"
through "K" will teleport you to an acid-floored, oblong
chamber to the northwest of the courtyard.  If this
happens, quickly walk forward (east), and a panel will
slide up in the middle of the east-side wall, allowing you
to exit the chamber.  When you exit, you can turn right
(south) to head back to the courtyard, if desired.