The Emptiness is essentially the Void or Limbo of the Underground, being located in an unknown spot that is said to be between Waterfall and Hotland. This is the dimension where certain Monsters go do in certain circumstances, due to their feelings or wants making them not satisfied with life as a whole. In here, they are in a state where they barely even exist to the rest of the world, ignored and forgotten.
The Emptiness was always in the Underground, before the Monsters were even down there due to the Barrier. It saw no use at all, for all Monsters on the surface were satisfied, and everyone is at peace. However, this all changed when Monsters were put into the Underground by the Humans. The first victim to go into the Emptiness was Lora, who was overridden with guilt from the War. She was declared the ruler of this realm... and she voluntarily stayed as a glitch, immortal and frozen in time.
The Emptiness was soon to trap more victims over time... some famous, some not-so-famous. The most famous example since Lora is W. D. Gaster, who had a rather interesting entrance. It is said that one of his experiments had gone rogue, and thrown him into the CORE, effectively scattering his remains across space and time. These remains soon collected back in the Emptiness, where he stands as the most anomalous of the bunch.
This dimension will only consume more in such a limbo... and it is unknown if there is actually a cure to such a state of the character. Time will only tell... it is known however, that these beings have been sighted in the real world before. Maybe they aren't truly forgotten after all...
The Emptiness is an empty black space located in an unknown area between Waterfall and Hotlands. This empty space is dotted with several unusual specimens, which are glitched from their status in this location. The ground appears to be nothing at all, but is as solid as a wooden floor.
To enter the Emptiness without becoming a glitch, one must traverse across a giant pool of lava into the Emptiness. Remaining in the Emptiness for an entire week will turn you into a glitch, so don't stay too long. There are other ways to enter the Emptiness, but these will cause you to immediately turn into a glitch:
- Falling into the CORE. (You will appear in there about one year later)
- Dying as an Amalgamate.
- Setting the "fun" value to 66, and entering Primum Castellum's market.
- Dying of a sickness, and still having unfinished business to do.
Lora was the Duchess of the Gorgons, who was actually quite the beautiful individual. Before the War, she was an ambassador to represent the Monsters as well. She met a man called Natis Prosec in the markets of Primum Castellum, and effectively formed a frienship with him. This soon became a romantic relationship, until the conflicts between Humans and Monsters began. When the Monsters were trapped in the Underground, she was ridden with guilt, thinking that she was one of the main causes for some reason. She has retreated to the Emptiness ever since then, being the ruler and first glitch of the area.
Gaster was the Royal Scientist before Alphys, who had created the CORE facility in the Underground. He had participated in many anomalous experiments, some of which had quite some significance to untold parts of the Underground. He was however killed by his last experiment, who had gone rogue and thrown him into the CORE, scattering his remains across space and time. He was soon recollected in the Emptiness however, and he resides there as a prominent anomaly.
The main entrance to the Emptiness is actually a giant lava pool located somewhere between Waterfall and Hotlands. This lava pool is too large to leap across by any means, and the air a number of feet above the lava pool is far too hot for anyone to fly across. The main way to cross this lava pool is to utilize an invisible path, which is almost always in a random pattern. It can be exposed, but not for too long. It's said that Lora is capable of changing the path when she feels like it, so memorizing isn't the best approach to this.
In the far-back of the Emptiness is Lora's Home, which is way too far away to be observed from the entrance by any means. Lora's home is actually just a wall, which has a fireplace, a painting of Natis Prosec, a closet full of Lora's clothing, and a weapon rack with some different knick knacks. There is also a soft rocking chair built for a Gorgon like Lora, and there is usually also a case full of Pomegranates nearby, as well. Usually, entering this area will soon result in the second and tougher battle with Lora.
Credit goes to TobyFox for making Undertale.