Beat Doom II: No Rest for the Living level 8, Tomb of
Malevolence:

When you first arrive on this level, you'll be at the
southeast corner of the map, facing northwest, and at your
feet is a short flight of narrow steps leading down.
There are Medikits on the floor nearby; pick them up now if
your health is low.

PLASMA RIFLE (SECRET 1 OF 3)
----------------------------
From the level's arrival point, go down those steps, turn
right, and go up the shallow flight of steps ahead of you.
At the top, look to your right for a pair of window-like
indentations in the wall, featuring blood-covered panels.
Walk up to the left-most of these two panels, and activate
it like a switch.  The panel will drop down revealing a
tiny chamber with a switch on the back wall.
Activate that switch, then step back and look to your left
(northeast) for a new opening in the wall next to you.
This is one end of a short tunnel, where a plasma rifle and
10 blue health bottles can be found.  At the far end of the
tunnel there is also a Computer Area Map.
This tunnel is one of three areas on the level that affect
the secrets-found score.

Return to the arrival point and proceed northwest, until
you come to a large demon-faced panel.  Open it, go
through and pick up the blue Mega-armor vest.  Open either
of the demon-faced panels located just past the armor, and
step through.
Pick up all the rockets and the rocket launcher you'll find
here.
Just behind the rocket-launcher is a switch that, when
activated, will cause the floor to begin descending.  Note
that when it starts dropping, you will not be able to
return to the area you were in a moment ago, until later.

"TALL" ROCKET EXPLOSIONS
------------------------
After picking up the rocket launcher and activating the
switch, the floor will begin dropping down into a larger
room, where several Imps await.
It is possible, though sometimes tricky, to damage or kill
some of these Imps before they come into view.
Rocket explosions in classic Doom games are "infinitely
tall", meaning that targets at any vertical distance from
the impact point are affected the same way... In essence,
the explosion is treated as if it is an infinitely tall
column, with a higher concentration of force along its
entire vertical core.
Because of this effect, as the floor is lowering you can
try shooting rockets into the nearby walls to damage or
kill some of the Imps which are standing near those walls,
but far below you.  (Remember not to get caught in your own
rockets' splash damage.)
As the floor is dropping, try standing at the end of the
chamber opposite the switch, facing northwest (towards the
switch), and firing rockets at the north and west walls,
and/or other walls as they become exposed while the floor
drops.  This can sometimes allow you to strike down a few
of the Imps before they have a chance to attack you.

Once the floor has lowered you'll be in a larger chamber
and surrounded by Imps, with more approaching from tunnels
to the north and west.  This is where "strafing" is a very
useful tactic for sidestepping fireballs, while pressing
your own attacks.
If you have the choice, you may want to switch from the
rocket launcher to a shotgun, chaingun, plasma rifle (which
first appears on level 4) or BFG 9000 (which first appears
on level 6, and again on level 7).

THE CYBERDEMON
--------------
Aside from waves of Imps, the only other enemy type on this
level is a single Cyberdemon, which will begin pursuing you
as soon as it hears or sees you.
A Cyberdemon typically takes 40 or more rockets to kill, or
two or more close-range BFG hits to dispatch quickly.  (Of
course, like any monster a Cyberdemon can also be killed
with bullets, shotgun shells, or even punches and chainsaw
attacks.)
A Cyberdemon is armed with a rocket launcher, and typically
fires in 3-round bursts.  The initial narrow confines of
this part of the level make it hard to dodge rockets and
their splash-damage effects.  Fortunately there is a useful
power-up here to provide some protection.

POWER-UPS (SECRETS 2 AND 3)
---------------------------
In the southwest quadrant of the main, maze-like combat
area, along the level's exterior perimeter look for a place
where the north end of a north-south wall meets the east
end of an east-west wall, to form a convex corner of red
brick, which is bordered by tall vertical bands of brown
metal and rivets.
Activate the banded section of red brick, and it will begin
to slowly drop down into the floor, to eventually reveal a
Berserk Pack and 3 green armor bonuses.
Activate the wall behind the Berserk Pack, and it will also
begin to drop into the floor, revealing an Invulnerability
Sphere, which grants you 30 seconds of protection against
all enemy weapons and melee attacks.
The small areas of floorspace under each power-up count as
score-affecting secrets.

ADDITIONAL ORDNANCE
-------------------
You can find switches scattered around the main, maze-like
combat area.  Ignore the switches on the exterior/perimeter
walls for now.
If you activate the switches on interior structures, the
structures will slowly drop down into the floor to reveal
various weapons (chaingun, super shotgun, plasma rifle),
some ammo, armor, and a backpack (the only backpack among
all of the "No Rest" maps).
At higher Difficulty levels, lowering these structures will
also release more Imps.

THE EXIT
--------
It is not necessary to kill the Cyberdemon (or any monster)
to exit the map, but it is recommended to clear out as many
enemies as possible before attempting to leave.

Go to the northern-most perimeter of the level, turn left
and head west until you come to a corner where you'll find
a switch on the wall, and activate it.
The northern-most wall will begin to drop down, revealing a
long, narrow east-west strip of flooring, just in front of
another long wall running along the north edge of the map.
Follow that wall east until you come to another corner with
a switch on the wall.
Activate this switch, and a long east-west staircase will
begin to emerge, running up along the perimeter wall.

Follow the steps to the top, and activate the switch on the
wall there.  That wall will drop down, revealing another
crowd of Imps.  Dispatch them and proceed up and around the
corner a few paces, to the highest spot you can reach.
You'll be standing right next to a red torch.  Turn to face
east (with the torch to your immediate left) and you'll see
a rectangular platform ahead and below you, with another
red torch at its far-left/northeast corner.
Walk or run (remember your Run button) to jump to that
platform.
(If you miss the jump, or the following ones, simply return
to the long staircase to the north, and try again.)

Once you're on the platform, turn right/south, and you'll
see another long platform with some wide steps at the far
end, leading up.
Run to jump onto that platform, walk up to the top step and
turn left/east.
You'll see another red torch (or a pair of them) ahead of
you, located just above a red teleporter pad.  Run to jump
to that pad, and you'll be teleported back to the level's
starting area.

You'll appear on a teleport receiver that is just above and
behind the spot where you first appeared on this level.
From here you can simply walk forward to a pedestal in the
middle of the room, where a new, short and steep staircase
now leads up to an exit portal at the top.

Note that, once you teleport back to the starting room, a
new teleporter booth will open down in the main combat
area, near the descending floor where you picked up the
rocket launcher.
Players and Imps can use this teleporter; the Cyberdemon is
too large to step inside.

To watch an example of beating this level at Ultra-Violence
difficulty, click here for a YouTube video.