How to exit PSX Final Doom level 28, Baron's Lair:

From the level's starting point in the central courtyard,
enter the small brown door to the west (Automap west).
Go down into the mud pit ahead of you, and Activate the
switch you'll find there.
The walls to your left and right will drop down, uncovering
another switch to the northwest, just around a corner.
That switch will open a small door behind you, leading to
stairs which go up and around to the red key (out and to
your right).
Grab the key and step on one of the nearby teleport pads to
get back to the door that leads to the central courtyard.
From the courtyard, go through the red-keyed door.  Then,
go down into the wide pit ahead of you to find the blue
key on the ground.  Grab it and go back to the courtyard.
Go through the blue-keyed door and you'll find a switch on
the ground ahead.  Activate this switch to lower the wall
in front of you, revealing a long north-south chamber.
Go south until you reach the far wall, then turn around to
face north.
You'll find switches to your left and right, recessed into
the backs of two supporting structures.
Activate both switches, then head back out to the central
courtyard.
You'll find that the wide door on the east side of the
courtyard is now open.  Go through that door and take note
of the two pedestals that are up ahead and to your left and
right.  (Revenants may be standing on these pedestals.)
Continue east until you get to the stairs ahead.  Up the
stairs and to your left is a switch; Activate it.
Go back down the stairs and go right, into a newly-opened
section, and walk west.  You'll see a switch in the corner.
Activate it to open up a new southern section of this room.
Go south into the new section, and look for a switch in the
middle of the southern-most wall.
Activate that switch and QUICKLY run out to those pedestals
where the Revenants were standing.
The switch you just activated opens up the two pedestals,
and inside each pedestal is another switch.
The pedestals remain open for only a couple of seconds, and
then close up again.  You'll have to activate each of these
pedestal switches in order to open up a path to the exit.
Once you've activated both switches, go back up the stairs
to the east, and you'll see that a door has opened to your
left... Go through and follow the path around to the exit.