Get to the keys/exit on PC Plutonia map Odyssey of Noises:

When you first appear on this map, you'll in a building
near the middle of the east edge of the map.

RED KEY
-------
Dominating the south end of the map is a wide, red canyon.
Along the western edge of that canyon is a series of tall
rectangular pedestals.  These form a crude stairway that
leads up to a building located near the middle of the south
edge of the map.
Go up into that building.  As you enter, turn left and look
for a closed door nearby in the corner.  Open it to reveal
the red key.  Grab the key, and a narrow panel will rise up
in the west wall nearby, revealing a switch at the back of
a small opening.  Activate that switch and step out of this
building.
Go down back the pedestal steps and head to the northeast
corner of the map.

YELLOW KEY
----------
Once you have the red key, look at your Automap.  Find the
fourth building down from the top of the east edge of the
map.  This building can be recognized by a curving wall at
its southeast corner.
Go to the northeast corner of this building, and look for a
stairway leading up.  Go up and around to the right, and
you'll see a passage leading north, across a gap, to the
next building.  Run to jump across that gap, then look for
a wide, diamond-shaped window in the north wall.
Run to through that window to jump to the roof of the next
building.
Walk to the northwest corner of this roof, and grab the
yellow key you'll find there.

BLUE KEY
--------
Once you have the yellow key, look at your Automap.  Look
for the single long road that runs east to west across the
middle of the map.
Near the middle of the map, this east-west road is bisected
by a north-south road.  From that intersection, follow the
road north, and look for a yellow-keyed door on your left.
(This door is just behind some narrow pillars running along
the east side of a building.)
Open that door and Activate the switch you'll find inside.
Turn around and walk back through the door.  Turn right and
head south, back down the road to the intersection near the
middle of the map.
At this intersection, turn left and follow the road east,
until you come to another road on the right, leading south.
Go south down that road, passing the first door in a
building on your left.  Continue south a few paces until
you come to the second door on your left.  This door is
between a pair of small open windows.
Open that door and grab the blue key you'll find inside.

THE EXIT
--------
Once you have the blue key, look at your Automap.  Find the
second building down from the top of the east edge of the
map (this is the same building from where you picked up the
yellow key).
Just west of that building (across the street) is another
building.  In the east wall of this building is a recessed
area, with four square pillars arrayed along a curved wall.
Between the back two pillars is a curving staircase that
leads to the roof.
Go up those steps, and Run north to jump to the roof of the
next building.  (You may have to back up a little to get a
good running start.)
Now turn left, and Run west to jump to the roof of the next
building.
Run west again, to jump to the roof of the next building.
Look for a blue-keyed door between a pair of hanging blue
banners, and open it.
Step through, into the wide hallway, and look for a switch
nearby on wall to your left.  Activate it, then look for a
second switch over at the other end of this hallway, and
Activate that one as well.
Step back out through the blue-keyed door and turn left to
face north.  Step north to drop down off this building, and
you'll be on an east-west road which runs along the north
edge of the map.
Turn left and head west along this road, until you come to
another road on your left.  Head south down that road.
When you come to a 4-way intersection with another road,
continue heading straight (south), and continue south past
the next short road on your left.
You'll come to a large, dark brown building on your left.
In the west wall of this building is a tall opening between
a pair of hanging banners.  Head up the steps there and go
into the building.
Ahead of you is a wide, deep dropoff.  Look to your right
for a series of narrow pillars rising up from below.  These
form a temporary path leading southeast to a window-like
portal at the southeast corner: The level's exit portal.
Warning: These pillars sink down as you step across them.
Run across the pillars and into the exit.
(If you fall off the pillars, quicky Run to the northwest
corner of the lava pit, and step on the teleporter there.
You'll reappear at the top, where you were a moment ago.
Look for a newly-revealed teleporter booth in the nearby
wall, and step in.  You'll reappear in front of the exit
portal; simply walk in.)

Done!

PC Plutonia players can access a demo that shows how to get
to the keys and the exit on this level, by clicking here.