E3M7: Limbo (Doom)

E3M7: Gate to Limbo is the seventh map of Inferno in Doom. It is referred to as Gate to Limbo on the intermission screen. It uses the music track "Waltz of the Demons". The name obviously comes from Dante Alighieri's The Divine Comedy, where Limbo is described as the first circle of Hell, a somber place where the unbaptised souls dwell (Canto IV). The par time is 2:45.

Walkthrough

 * 1) First head to retrieve the blue skull key.  To obtain it, head north and then west along the the semicircle platform surrounding a large circle of blood in the large room.  When there is a fork in the path, head left and then south, all the way to the bottom southeast corner of that area where the blue skull key is resting on a small platform surrounded by blood.
 * 2) Next head back to the large circle room with blood and the "semicircle path," this time heading east to a room with two doors that require a blue key.  The door on the south leads to a secret which requires the red skull key, while the door on the north leads to the underground blood maze which holds the red skull key near its end.
 * 3) Head this way and fall down the hole which takes you the first "rest stop" of the blood maze.  There are two of these "rest stops" along the maze and each holds serveral radiation suits to protect you while you search the labyrinth.  The first rest stop has two directions, west and east.  The east leads to a secret area, while the west leads to the red skull key at its end.
 * 4) Take the west route to lead to eventually lead to another "rest stop."  Then continue along the labyrinth to head towards the red skull key.  When you reach a path to a "warp" along the way, DO NOT GET IN.  Take the alternate path beside it and that will lead you to the room with the red skull key.  If you were to get into that warp, you will teleport to the area where you recieved the blue skull key and will have to make your way all the way back here again.  However, once you recieve the red skull key and have opened the door behind it and activated the switch, this is your only option.
 * 5) The warp will lead you back to the general area where the blue skull key was originally.  You may activate the switches around the walls to open secret rooms in the area, of which one contains a star-shaped blood pool with a "supercharge" in the middle of it.
 * 6) It's time to get the yellow key.  So, to do this head back to the large circular blood room in the middle of the map and get ready to head across the harmful blood.  Contrary to what you might be thinking, you are not supposed to head to the door in the center of that particular circular room, but instead are supposed to head to the room directly north of that one (which contains even more blood to cross).  This room has a small section in the bottom right corner which houses a radiation suit to cross, should you need one.  Head to the pillar with a warp inside it in the upper left corner of that room.  The warp teleports you to the area where the stage exit is.  It also has a switch which you must activate to get the yellow key later.  Head back in the warp and when you teleport back to the room with the blood all over the ground, enter the right most pillar with the warp inside to warp back to that same room you were awhile ago.  This time, however, the yellow key is accessible to you now that the land has been raised.  Grab it and return to the warp.
 * 7) Now you must head back to the main circular blood room and head to the west where you will then head south to the southwestern-most corner of the map (considering the star-shaped secret room containing the "supercharge", go a little east, then some south and finally some west).  This is yet another blood-filled room with a warp inside another pillar at its end.  Run across the blood to this warp.
 * 8) It teleports you to a room where you must activate a switch, but not much else.  Activate this switch to create a land mass for you to cross in the adjacent room.  Head back in the warp.
 * 9) Return to the large circular blood room and now you may enter the warp in the middle of the room.  This leads you to the adjacent room mentioned previously, but now has a land bridge for you to cross.  Cross the bridge to a room requiring the yellow skull key.  Inside, activate the switch.  This creates a land bridge to the EXIT door, so that you may go through.  Head back to the warp and from the large circular room, go west.
 * 10) At the first fork in the road on the west route, head north and then follow the path to yet another blood-filled room (once again considering the star-shaped secret room with the "supercharge", go north, then some east to find it).  In the northeast corner of the room is a pillar with a warp inside.  Go inside it.
 * 11) You will be teleported to the last stretch of the level.  Use the yellow skull key to open the door and head straight forward to the EXIT door.

Secrets

 * 1) In the southwestern corner of the map is a pool of blood with a switch in it. Flipping this switch opens the large octagonal structure in the area to the north. Inside the structure is a pentagram with a soul sphere on it that counts as a secret.
 * 2) Directly to the southeast of the aforementioned pentagram structure is a vaguely hexagonal green marble structure. Walk around the back of this structure and two of its walls will open, revealing a secret area.
 * 3) In the northeastern corner of the map is a maze of blood-filled tunnels. From its start, head right, right, left, then right. You'll end up at a secret platform with a BFG.
 * 4) After flipping the switch next to the red skull key in the blood maze, return to the central area after taking one of the teleporters in the maze. Go through the southern of the two blue doors in the east. In a nearby alcove is a switch; press it to lower a wall back outside. Flip a second switch behind the newly lowered wall to raise a bridge to the "teleport tube" in the southeastern corner of this room. Go through that teleport to be taken to a secret area.

Bugs
A set of 4 shotgun shells (Thing 62) and an energy cell (Thing 123) have no flags set for any of the difficulty classes, so they do not actually appear in the level.

The switch that is tagged to lower the wall with the Baron behind it in the maps south east corner is also tagged to the two blue doors along the east side of the map. However, because the floors of these doors are already the same height as the surrounding floors, this has no ill effects on the map.

Linedef 971 above the north west teleporter in the blood maze lacks an upper texture on one of its visible back sides, hence producing a hall of mirrors effect.

Routes and tricks
You can jump across two gaps while preparing the exit.
 * The switch filling the gap towards the yellow key is optional, but if you press it anyway, you can easily run across the blood pit to reach the key. Otherwise, you can simply jump the gap by straferunning.  This saves slightly on time, requiring only one teleport.
 * You can jump the gap leading to the yellow key door by straferunning as well. This saves you from going to the south-west corner of the map.

Records
The Compet-N records for the map are:

Trivia

 * A dictionary defines Limbo as "a region on the border of Hell or Heaven, serving as the abode after death of unbaptized infants and of the righteous who died before the coming of Christ".
 * This was originally supposed to be the first Hell level in Tom Hall's original design plans for DOOM, which would make logical sense given what Limbo is. It is possible, however, that the full name of the map, "Gate to Limbo," refers to how the player is on the (heavily demon-guarded) border to Limbo which is in Hell, rather than being "between Hell and Heaven."