Access the keys and exit Doom 64 level 22, Burnt Offerings:

When you first appear on this map, you'll start in a small
cave.  Exit the cave and go right, through opening that
leads to a large open courtyard.  Go into the courtyard and
head to the opposite side.
You'll enter a large, dark rectangular room, where an array
of square pillars stretch from floor to ceiling.  Watch out
for Spectres lurking here.
As you first enter this large dark area, turn left, and
look along the left-hand wall for a door.  Open it and step
through.  You'll be at the top of a stairway.  Go to the
bottom of the stairs, and you'll see a closed red door
ahead of you on the far wall, in the corner.  Ignore this
for a moment and turn left, into another rectangular room.
At the far end of this room is a switch on the wall;
Activate it to open that closed red door.
Go through that now-open door and go up the stairs.  These
stairs wind their way up and around the end of the room you
just left.
Halfway up the stairway is a switch; Ignore it for now.
At the top of the stairway you'll see a small square window
ahead, and another switch next to it.

BLUE KEY
--------
At the top of the stairs you can see the blue key through
the small square window.  The key is at the top of a tall
pedestal, which is just outside and slightly to the right
of the window.
The switch next to the window will temporarily drop the
pedestal down to the floor below.
There are two main ways to get the blue key:
1) Go back halfway down the stairs, then Activate the first
switch (this opens a wall panel next to the small window at
the top of the stairs), then quickly Run up the stairs and
Activate the switch to drop the pedestal, then jump down to
grab the key; Or
2) Activate the switch next to the window, and very quickly
back up and side-step to the left to step out of a window
along the side of the stairway, then run to get the key.

Just to the left of where you pick up the blue key are some
stairs.  Go up the stairs and look for the blue-keyed door
on your left, and step through it into a large square room.
As you enter the room, four small obstacles that surround a
rocket launcher in the center of the room will retract into
the floor.  Ignore the launcher for the moment, turn left
and search the wall ahead for a hidden panel. It will drop
down when activated, revealing a switch.  Activate that
switch, and the obstacles around the launcher will return.
Pick up the rocket launcher, and a brief barrage of spikes
will shoot out towards the launcher, but will be deflected
away by the obstacles.
When the spike attack has stopped, a door opens in the wall
opposite the blue-keyed door.
Go through that door and head right, and continue around
the corner until you get to a switch at the far end of the
corridor.  Activate the switch, then turn around and go to
the opposite end of this corridor (past the doorway you
came through a moment ago), and Activate the switch you'll
find there.
Now go back into the square room where the rocket launcher
was, then back out through the blue-keyed door, and down
the steps.
At the bottom of the steps turn left and you'll see another
stairway going up.  Go up to the top and open the door on
your left.  Step through, and you'll be back in that large,
dark rectangular room with the square pillars.
Go straight ahead until you come up to a wall, then turn
right and follow along this wall until you come to a newly
opened passage on your left.
Go through the opening to enter into a long dark room which
has antechambers branching off to the left and right.

YELLOW KEY
----------
Go to the far end of this room, where you'll find rows of
bright candles clustered together.  The yellow key is at
the back wall, in the middle of the cluster of candles.

As you pick up the yellow key, turn around and go back to
the far end of this room, and back through the opening.
You'll be back in that large, dark rectangular room with
the square pillars.  Turn right and walk several paces
forward.
Turn left and go to the far wall, and look for that door
that you came through a few minutes ago.
Go through that door and back down the stairs.  At the
bottom, look for an open doorway straight ahead in the far
corner.  (This was the red door that you opened before.)
Go through that doorway and follow the winding stairway all
the way to the top.  At the top, make a U-turn to the right
and follow the corridor until you come to a yellow-keyed
door on your right.
Go through that door and follow the long corridor until you
get to another closed door.  Open it and step through.
You'll be at one end of a large "asterisk"-shaped area,
where eight corridors meet at one common center.  In front
of you will be a square barrier.  Step around it and walk
straight to the center of the "asterisk".

RED KEY
-------
The red key is at the center of the "asterisk", where the 8
corridors meet.  Pick up the red key, and 8 nearby barriers
will rush up to surround you.  At the barrier in front of
you (as you approached the key), a switch will appear.
Activate the switch and the barrier behind you will open up
momentarily: Quickly run back out from between the barriers
to avoid being crushed by a section of the ceiling.

There is a switch at the far end of one corridor, opposite
from the corridor with the door you opened a minute ago.
That door is now closed.  This switch opens it, but only
for a moment.
Activate the switch and quickly Run to the far corridor and
go through that door before it closes again.
If you have trouble getting to the door in time, you may
find it useful to use a combination of Run plus Strafe.
(This "strafe-running" maneuver moves the player character
at an odd angle, but yields a speed slightly above that of
plain running.)
Once you make it through the door, follow the corridor back
to the yellow-keyed door up on your right, and go through.
You'll step into a corridor you were in a few minutes ago.
As you walk down the corridor, you'll notice a pair of
balconies on your right which overlook the courtyard.  Step
down off either of the balconies, and proceed straight to
the far side of the courtyard.

THE EXIT
--------
In the courtyard, look for the red-keyed door.  It's in the
middle of the wall on the opposite side of the courtyard
from the balconies.
Through the red-keyed door is a small chamber, and on its
back wall is the Exit switch.