How to access the keys and the exits in TEETH.WAD, map 31:

There are two exits in this level: a normal exit (which
leads to map 16 in the local Doom II Wad file), and a
"secret" exit (which leads to map 32 in TEETH.WAD).

To get into the normal exit, you won't need any keys.  To
get into the secret exit, you'll need all three keycards
(red, yellow, blue), and you'll also need the assistance of
an enemy monster.

Note: To access the secret exit in this level (without
cheating), do not use the "-nomonsters" command-line
parameter when starting the game; Monsters must be present.

You begin the mission on top of a wide, cylindrical
elevator in the raised position.  Surrounding the elevator
are 8 passages, leading off in each of the 8 common compass
directions (north, northeast, east, southeast, etc.).

On the Automap (and sometimes in first-person view) you may
notice some stylized numerals that mark the floor and
ceiling of each of these 8 passages.  Passage "1" leads
north, and its entrance is located at the bottom of the
main elevator shaft.  Passage "2" leads northeast, and its
entrance is somewhat higher in the elevator shaft.
Subsequent passages are higher up the walls of the elevator
shaft at regular intervals, with passage "8" at the top of
the elevator shaft.
Part of the way down passages 2 through 8 are vertical bars
that prevent further progress in those directions.

You will need to start the mission in passage 1.
To the left of the entrance to passage 8 is a red switch on
the wall, which will cause the elevator to drop slowly to
its lowest position, where you'll find the entrance to
passage 1.
Enter into passage 1 and head north towards the far end.
As you head north, vertical bars may drop down in the
passage, preventing further progress north.  The bars in
passage 1 will automatically rise up again about 30 seconds
later.
Continue down the twisting halls of passage 1 until you get
to a metal door.  Go through the door to small square room.
Look on the east wall of this room for a switch, and
activate it.  The wall section where the switch is mounted
will drop down, revealing a small "closet", with another
switch on the back wall.  Activate this switch.  (This will
raise the vertical bars in passage 2.)
Head back to the elevator shaft.  Note that as you walk up
to the cylindrical elevator from any passage, the elevator
will automatically drop down to its lowest position.  If
you step up to the elevator and it does not lower, wait a
moment, then back up a couple of paces, away from the
elevator, and then step up to it again.

Get on the elevator and, when it starts rising again, get
off at the entrance to passage 2.  (If you miss this
entrance, ride the elevator to the top, and hit the switch
near passage 8 to lower the elevator again.)
Walk to the end of passage 2 and look for a dark open
doorway on your left.  Step through into a darkened chamber
and you'll notice three teleporter booths.  Step into the
middle (red) one.
You'll be teleported into an area just south of passage 5.
You'll be at the north end of a narrow, raised pathway.
This pathway is intersected in the middle by a similar
raised pathway, and these two pathways form a plus-shaped
structure.  There is a rocket launcher and other useful
items nearby.
Look for a red switch where the pathways cross (it will be
at the northeast corner of the intersection), and activate
it.  (This will raise the vertical bars in passage 3.)
Go back to the north end of the plus-shaped structure and
step on the teleporter pad there.  You'll be teleported
back to the dark chamber with the three teleport booths.

RED KEY
-------
As you step off the red teleporter pad, look for a secret
panel ahead on your right.  It will be a diagonal panel in
the dark room, at the doorway right before you step back
into passage 2.  When you activate the hidden panel, the
wall rises up, revealing a small chamber to the west with a
red teleport pad.  Step on.
You'll appear back in the area just south of passage 5.
You'll be in a dark chamber, raised up a bit from floor
level, with a window that looks north upon the plus-shaped
structure mentioned above.  The red keycard is here in this
dark chamber; grab it.

Step down through the window.  You'll be near the south end
of the plus-shaped structure.  Look on the east side of
this southern end of the "plus" for a vertical strip that
runs floor to ceiling.  This tall panel is a different
color and texture than that of anything else in the room.
Activate this strip like a switch, and it rises up,
revealing a switch underneath.  Activate it.  (This will
remove one barrier which blocks access to the blue key,
which you can get later on.)
Now go to the northeast wall of this room, and look for a
pair of recessed "steps" built into the wall: one wide step
near floor level, and, above and behind it, a narrower one.
On the narrow step is a rocket, and behind that rocket is a
switch on the wall.
Walk up to the wide step at ground level and activate it to
cause it to drop down.  Get on before it rises again.  Then
activate the smaller step and it also drops.  Get on that
one and ride it up; then activate the switch on the wall.
(This will raise the vertical bars in passage 6.)
Now walk back down the "steps" to ground level.

YELLOW KEY
----------
Note that on the northwest wall of the room (see "RED KEY",
above) there are recessed "steps" identical to those on the
northeast wall.  Whenever you activate one of the steps in
the northeast wall, the counterpart of that step drops down
in the northwest wall.
What you want to do now is activate both steps on the
northeast wall, and then immediately run for the steps in
the northwest wall, and get on the narrow northwest step
before it rises up again.  (Remember that Run mode is
typically enabled by holding down a Shift key.)
This maneuver may take a few tries to accomplish
successfully.
Once you're on the narrow top step in the northwest wall,
turn northwest and activate the wall panel in front of you.
It opens, revealing a small rectangular chamber.  Enter the
chamber and walk around the corner to your right, where
you'll find the yellow keycard on the other side of a
narrow partition.

Exit this chamber through the same wall panel you entered
from.  Walk down the "steps" to ground level, and head for
the door at the north end of the room.  Go through the door
into passage 5.  If you find vertical bars here blocking
your way, simply activate them, and they will rise
permanently into the ceiling.  Go back to the elevator and
get on.

BLUE KEY
--------
Once you've activated all switches mentioned above, take
the main elevator and get off at the entrance to passage 3.
Walk to the end of the passage and walk east through the
door there.  You'll enter into a small circular room with a
short square pedestal in the center, and a pair of switches
on some "steps" on the east side of the room.  Walk up to
the lowest of these steps and activate the switch there.
This will cause the pedestal in the center of the room to
drop down.  Get on it before it rises again.
When the pedestal has risen up, Run east to land on top of
the step where the first switch was.  This allows you
access to the second switch on the next step up.  Activate
it to raise the vertical bars in passage 4.
Go back out of this room, and head west, back down passage
3 to the elevator.
Ride the elevator and get off at the entrance to passage 4.
Walk down the passage, past a door on your left, to an open
doorway at the end of passage 4.  You'll enter into a
chamber where there's a window ahead of you, a closed door
on your left, and a large glowing panel in the wall to your
right.  (Behind this glowing panel is the blue keycard, but
it is not yet accessible.)
Go through the door on your left.  You'll enter into a tiny
chamber with three doors: the one you just came through,
another closed door ahead of you, and an open doorway to
your left.  Go north through the open doorway.
When you step all the way through this doorway, the glowing
panel (back in the chamber at the end of passage 4) opens,
allowing access to the blue keycard.  Grab it.

(There is a switch nearby that will open the bars blocking
passage 5, if you did not already open these bars manually
from the room just south of passage 5.  To get to this
switch, go back to the small chamber with the three doors,
and again step north through the doorway that triggered the
opening of the glowing panel which concealed the blue key.
Now head right, northeast, to a closed silver door.  Go
through and turn right/east into a darkened rectangular
room with "candles" on the floor.  Step into this room and
follow the candles to a switch in the middle of the south
wall of this room.  Activate it to raise the vertical bars
in passage 5.)

Head northwest back up passage 4 to the elevator, and get
on it.
If you have not already been inside the room which is south
of passage 5, go there now, and activate the switch in the
northeast wall of that room (see the last paragraph under
"RED KEY" for details) before proceeding to passage 6.
Get on the elevator and ride it up to the entrance to
passage 6.  Head southwest down passage 6 to a room at the
far end which contains five tall, narrow cages.  At the
back of this room you'll find a switch in the middle of the
southwest wall.  Activate it.  (This will raise the
vertical bars in passage 7.)
Head back to the elevator, get on, and ride it up to the
entrance to passage 7.
Head west down passage 7, past a door on your left, to
another door at the far west end of the passage.  Go
through this door and you'll see a tall, rounded metal
pillar in front of you.  This is an elevator.  Step up and
activate it to cause it to sink down into the floor.  Get
on and ride it all the way up.
When the elevator has risen to the top, turn to face north.
You may see an Imp or chaingunner in front of you, in a
small niche in the wall.  Kill it.  (This will help allow
you to run across the top of the niche in a few moments.)
From on the top of the elevator, turn to face west and
you'll see some shallow steps in front of you, across a gap
of open space.  Run west off the elevator to get onto the
steps.  Go up the steps and turn right.  Walk east along
the platform which spans the north half of this room.
You'll see a gap (where the Imp/chaingunner was) in the
floor ahead of you as you walk east.  Run east to jump over
this gap, and look for a switch on the east wall of this
room, near a cluster of armor helmets on the floor.  Walk
up to this switch and activate it.  (This will raise the
vertical bars in passage 8.)
Jump back down to ground level, and, with the metal pillar
to your back, look for a door on the east side of the room.
Go through this door, and head east, back down passage 7 to
the map's main elevator.  Get on the elevator, and ride it
up to the entrance to passage 8.

Head northwest down passage 8 to a door at the far end.  Go
through and you'll notice a staircase ahead of you.  Walk
up to the "door" at the top of the stairs.  When you
activate this door, it will not open.  Instead, two panels
open up in the northwest wall of the room: one panel each
to the left and right sides of the staircase.  Go back down
the stairs, then turn and go to the northeast side of the
staircase.
Look for the opening ahead to the right on the northwest
wall.  Walk into this narrow passage, and activate the
panel at the far end (northwest end) of the passage.  A
piece of the wall drops down to reveal a green sphere: an
Invulnerability Artifact.  Grab it, and immediately save
your game if you haven't done so recently.
Now run around to the other side (southwest side) of the
staircase, and look for a passage off to the left side of
the staircase in the northwest wall.  This passage leads
northwest, and at the end of it is an Arch-Vile monster.

Do not kill the Arch-Vile yet if you wish to use the
level's "secret" exit.  At this point you can choose to
leave the level through one of its two exits.  See "SECRET
EXIT" or "NORMAL EXIT", below.

SECRET EXIT
-----------
Before proceeding, make sure that: A) you have all three
keycards, B) you've picked up the Invulnerability Artifact
you found to the right of the staircase in the chamber at
the end of passage 8, and C) you've saved your game at this
point.

What you want to do now is provoke an attack by the
Arch-Vile monster: Walk right up to it.
When an Arch-Vile begins to attack you, some flames will
appear around and above you for a few moments.  Then, as it
completes its attack, your body is jolted upwards into the
air.
A moment after the flames engulf you, begin to walk (or
run) southwest, away from the Arch-Vile, and towards the
raised open space in the wall in the southwest corner of
the room.  As the Arch-Vile completes its attack on you,
you'll be jolted into the air.  If you're moving towards
the ledge in the southwest corner of the room, the
Arch-Vile's attack may propel you up into this opening.
If you don't make it onto the ledge, go back and try again.
If necessary, you may wish to reload your saved game.  (If
the Arch-Vile attacks you when you're not invulnerable, you
may take significant damage.)
Once you're up inside this space in the southwest corner of
the room, move west/northwest to interpose the corner of
the wall between you and the Arch-Vile to prevent further
attacks.  Now look for a semi-camouflaged door in the
northwest corner of this small "cubbyhole" you're in.  It
will open when Activated if you have the yellow key.
Behind this door is another door, requiring a red key.
Open that door to find another door ahead and to the right.
With the blue key you can open this door, which reveals the
blood-red "secret exit" chamber.  Stepping into this
chamber ends the mission and then takes you to level 32 in
TEETH.WAD.  (Note that crossing the threshold of this
chamber door counts as 25% of the Secrets attainable on
this level.)

NORMAL EXIT
-----------
Kill the Arch-Vile monster (and the Imp hovering in the air
above it), and then look for a switch at the end of the
passage (on the northwest wall, behind where the Arch-Vile
was).  Activate this switch, and an elevator-like section
of the wall to your right will drop down momentarily.  Get
on before it rises up again.  When it rises to the top,
turn right to face a switch next to you on the southeast
wall.  (This opens the regular-exit door at the top of the
staircase.)
Now turn and walk northwest into a tiny square chamber.  On
the southwest wall is a switch.  Activate it, and the floor
just outside this chamber will drop down again, allowing
you out and back down into the room with the staircase.
Follow the stairs up to the now-open door at the top.  The
regular-exit chamber lies ahead.  Step in to end the
mission and resume the game on the next map: level 16 in
your local DOOM II Wad file.

PC Doom 2 players can click here to access a demo showing
how to find the exits on this level.