E3M7: Limbo (Doom)

E3M7: Limbo is the seventh map of Inferno in Doom. It is referred to as Gate to Limbo on the intermission screen. It was designed by Tom Hall and Sandy Petersen, and uses the music track "Waltz of the Demons". The name obviously comes from Dante Alighieri's epic poem, the , where Limbo is described as the first circle of Hell, a somber place where the unbaptized souls dwell (Canto IV). The par time is 2:45.

In the Atari Jaguar-based versions of Doom, this level takes the player to E2M9: Fortress of Mystery (known as Dis in those ports). In the Sony PlayStation and Sega Saturn versions of Doom, this level takes the player to E2M8: Tower of Babel.

Overview
This level is known for its multitude of teleporters, many in recognizable pillar structures, that take the player all across the map.

Essentials

 * 1) First head to retrieve the blue skull key.  To obtain it, head north and then west along 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 in the south leads to a secret which requires the red skull key, while the door in 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 to the first "rest stop" of the blood maze.  There are two of these "rest stops" along the maze and each holds several 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 teleporter 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 teleporter, you will teleport to the area where you received the blue skull key and will have to make your way all the way back here again.  However, once you receive the red skull key and have opened the door behind it and activated the switch, this is your only option.
 * 5) The teleporter 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 teleporter inside it in the upper left corner of that room.  The teleporter warps 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 teleporter and when you warp back to the room with the blood all over the ground, enter the rightmost pillar with the teleporter 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 teleporter.
 * 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 teleporter inside another pillar at its end.  Run across the blood to this teleporter.
 * 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 teleporter.
 * 9) Return to the large circular blood room and now you may enter the teleporter 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 teleporter 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 teleporter 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. (sector 84)
 * 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. (sector 98)
 * 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. (sector 80)
 * 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. (sector 119)

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 map's 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.

There are 33 known anomalies in this level's REJECT table.

Routes and tricks
The player can skip most of the map by rocket jumping on an upper marble edge in front of the exit door and using a lost soul as a surface for the rocket to explode against.

Current records
The Compet-N records for the map are:

The data was last verified in its entirety on November 21, 2012.

Player spawns
This level contains four spawn points:
 * 1) facing north. (thing 137)
 * 2) facing north. (thing 138)
 * 3) facing north. (thing 139)
 * 4) facing north. (thing 140)

Things
This level contains the following numbers of things per skill level:

Inspiration and development
A primitive version of this level appeared as E2M1 of Doom 0.5. It was originally meant to be the starting level of Episode 2: Lost in Hell mentioned in the Doom Bible. This level cannot be played in the 0.5 alpha, however, because it references non-existent textures, and this version of Doom will refuse to load a level that references invalid texture indexes for one-sided linedefs. If the level is inserted into Doom 0.4, it will be able to load and play (typing doom e2m1 into the command prompt), but it will crash immediately if a one-sided linedef that references a non-existent texture enters the player's viewpoint. The missing textures are indexes 132 and 133 (0x84 and 0x85 in hexadecimal, respectively), but no such texture index exists in any known alpha build. Doom 0.3 contains 51 valid wall textures (ranging from 0 to 50), Doom 0.4 has a total of 119 (ranging from 0 to 118), and the 0.5 alpha in which this level is included has a total of 128 (ranging from 0 to 127).

Trivia

 * In Roman Catholic theology, Limbo is a place where innocent souls exist temporarily until they can enter heaven, notably those of the saints who died before the advent of Christ (limbus patruum) and those of unbaptized but innocent children (limbus infantum). Aside from the Divine Comedy, it also finds mention in 's , where it likewise appears as a region between Heaven and Earth which is passed through briefly by Satan as he travels toward Eden.