"Limbo is the accumulated remains of a thousand dead worlds, timeless and infinite. Yet it is not a lifeless realm, because something old sleeps here, something that watches and waits. Think twice before you break the ancient walls within the dungeons, because whatever built them did so for a very, very good reason. There are eyes in the dark, and you are not supposed to be here."
- Quoted from the Dimensional Door Mod Page.
Limbo is part of the Dimensional Doors mod. It's an alternate dimension that can be accessed by dying (with some other methods) in the dimension you access through the use of the dimensional doors. It should also be noted that Monoliths are also capable of teleporting you to limbo as well. When you're teleported to Limbo, you'll spawn falling from the sky, but will not take fall damage you land on the ground (However, landing on something placed by a player character, such as a chest will inflict damage.)
It is not noted that should multiple people die in a server and land in Limbo that they will be able to find one another. The spawning points are easily in the thousands, even in the ten thousands making it difficult to locate one another in a timely manner, much less have the patience to really care to do so since leaving is easy.
How To Get In
Getting into Limbo is not difficult at all. There are various ways (Listed below) to access this dimension.
1. Enter an unstable door: When you enter an unstable door, you may enter limbo, but this method can also teleport you to other unintended locations.
2. Die in a pocket dimension: If you die in a pocket dimension, you'll automatically be teleported to limbo.
3. Break the walls in dimensional dungeons: There are Monoliths outside, and they are capable of sending you to limbo.
4. Go too deep into the pocket dimensions: This will eventually land you in Limbo. The door created to get in will not open for you to leave.
5. If you like to cheat a lot then first get to pocket dimension, then get Monolith spawn egg, summon him, and switch to survival if you don't have it already, you should appear in Limbo in no time.
How To Get Out
The best way to exit limbo is to explore until you find large pools of a liquid. These should be around Y:20. By walking onto these blocks you will be randomly teleported to a location in the overworld and you will keep all of your items. The other alternative is to die by starving to death. Or to kill yourself with potions such as instant damage. Doing any of these will return you to your overworld spawn, but you will lose all the items you had on you. You cannot create rifts within Limbo, making any doors or signatures you have useless here.