How to find the keys on level 29, Twilight Descends:

You enter this level in the southwest corner of the map.
This will be the universal starting point for finding each
of the keys.
Compass directions ("north", "east", etc.), can be
determined by viewing the Automap.  North is considered to
be at the top of the Automap screen.

Note: Monsters and secret areas are not included here.

BLUE KEY
--------
From the map's entry point, walk north, following the west
(left-hand) wall until you come to a stairway.  Go north
up the stairs, and go through the door at the top to enter
into a room with stacks of boxes on the floor.  Near the
west wall in the northwest quadrant of this room is a
single brown crate, separated from the rest.  On the south
face of this crate is a skull switch.  Activate it.  This
will cause some steps to raise up from the floor along the
north wall of this room.  The steps lead up to the tops of
some crates running along the north wall.  From there you
can walk or run south to jump to the top of the next
nearest crate.  Walk south a few steps along these crates
to a stone pillar which raises up to the ceiling, and is
surrounded by more crates on the floor.  Here, you can walk
along the tops of the crates around the pillar and jump
south or southwest to the tops of the nearby crates.  From
there jump down to the floor in the south side of the room.
Head for the southwest corner of the room, where a low,
small gray box sits alone on the floor in the corner.
Go stand on this box, and a lift drops down nearby to the
north.  The blue key is on the lift.  Grab it, and ride the
lift up to the top.
Just to the north of the lift is a skull switch on the
wall; Activate it.  This will cause a crate on the east
side of the room to sink into the floor, which in turn
allows a way back into the north side of the room, if
desired.  The skull switch you just Activated also opens a
teleporter booth in the southwest corner of the room.  The
teleporter pad transports you to the tops of the crates in
the northwest corner of the room.

RED KEY
-------
Note: You'll need the blue key before you can acquire the
red key.

From the map's entry point, walk north, following the
left-hand (west) wall until you come to a stairway.  At the
bottom of the stairway, turn right (east), and look for a
blue-rimmed wooden door, sunk into the wall of a gray
building.
Go through the door and continue east, up some low steps.
At the top of the steps is a rectangular room.  There will
be caged-in areas along the east and north walls of this
room.
Walk to the north end of the room, and turn left (west),
and look for a brown metallic lift near the northwest
corner of the room.  Activate the lift, get on and ride up.
Walk northwest a few paces, and you'll see the red Skull
Key in a square hole cut into the west wall.  To the right
of the key you'll see a wooden door in the north wall.  Go
through this door, and into a wooden hallway that stretches
north, down some shallow steps.
Midway down this hall is an area lit up by a torch.  The
light from the torch illuminates a panel on the east wall
of the hallway.  Activate this panel to open it, revealing
a passage leading east.  Follow this winding passage to
where it ends in a small dark room.  Look for a skull
switch on the south side of this room, and Activate it.
A section of the wall will open up just to the left (east)
of the switch.  Step through this new doorway, and turn
left, and follow the path east, then south to a skull
switch on the wall to your left, and Activate it.  Now go
back to the dark room you just came from, and from there
head back to the wooden hallway where the torch is.
Once back at the torch, follow the wooden hallway north,
down some steps, and at the end of the hall turn right
(east), and look for a nearby four-sided pillar.  On the
north face of this pillar is a skull switch.  Activate it.
Now, as you face the skull switch, turn 90 degrees right
and walk west, past a couple of pillars, until you get to
the west wall.  Turn left and walk south until you come up
upon a dark metal lift to your right in the west wall.
Activate the lift to drop it down, get on and ride up.  At
the top, enter the small chamber and turn left.  Take a few
steps south, and look for another skull switch on your
left, and Activate it.
Now go back and take the lift down into the dark room you
just came from.  When you get off the lift, turn right and
head south a few paces.  You'll see a large dark brown
metallic shape on the floor ahead.  To the left of that is
a final skull switch.
Activate the switch, and then Activate the metal shape next
to it, and it will sink into the floor.  Get on and ride it
up.  From there, head south up the steps, and look left to
see the red Skull key, which you can now acquire.

YELLOW KEY
----------
Note: You'll need the red key before you can acquire the
yellow key.

From the map's entry point, walk north, following the
left-hand (west) wall, past the staircase, until you come
to some vertical red bars.  The red key will allow you to
Activate the bars, which will rise up out of your way.
Proceed north until you see a lake of slime ahead of you.
Just at the edge of the lake, look right (east) for some
stairs behind a pillar.  Take the stairs up to a dark room
overlooking the lake.
You can jump northwest out of this room, to land on a flat
rock structure on the north side of the lake.
From here, head west to some stairs that curve up and
around north, to where the yellow key sits on a pedestal.
Activate the skull switch there to drop the pedestal,
allowing you access to the key.