Es ist ein wenig unglücklich umschrieben in HotS, ja 
Die „Voice of the Darkness“ lebt in der Leere.
Amon selbst ist später ebenfals in diese Ebene übergewechselt und verwendet ihre Enegien, für seine zwecke.
Dennoch ist er dahingehend nicht alleine.
Wie bereits schon beo WoW angemerkt, ist diese Energie nicht unbedingt zwangsläufig „bösartig“, sondern es liegt in ihrer Anwendung.
Viele andere verwenden z.B. ebenfals die Leerenenergie:
Die Nerazim
„The Void is not like the Khala. It does not draw us together and connect us in a blanket of warm feelings. The Void certainly does not offer itself willingly. A dark templar stalks the Void and, through will and discipline, forces it to give up its power.“
- Theromos
Sie sahen die Leere als etwas an, was einem „Afterlife“ nahe kommen würde.
Die Tal’darim
The Tal’darim believed that Amon resided within the Void, and it was only through his blessing that one was able to travel through it. It is from the Void that they draw energy for their bane blades, which are comprised of pure Void energy. In addition, they regularly use terrazine, a substance originally from the Void, to enhance their powers.
Wobei das Terrazine von allen Rassen in Star Craft für unterschiedlichste Zwecke genutzt wurde.
„It’s clearly related to vespene gas, but there are some very exotic organics added into the mix.“
„Any guesses what it’s used for?“
„Well it would definitely affect brain chemistry, so it could be used as some kind of a drug or stimulant I suppose.“
- Dr. Ariel Hanson and Jim Raynor discussing terrazine(src)
Terrazine SC2 Game1A canister of terrazine
Terrazine gas is a potent psionic reagent. It is sought by protoss, zerg and terrans alike. The protoss consider it „the Breath of Creation“ (literally translates as such via Khalani). The Tal’darim believe that terrazine is a gift from the xel’naga to allow communication with them.
Was die Xel’naga selbst angeht, so wohnen diese in Ulnar !
Einer Festung, der Pandamoniumfestung in Diablo nicht unänlich.
Einem Ort, welcher zwischen Den Dimensionen liegt
Cradle of LifeEdit
„In protoss legend, Ulnar took on mythical proportions, believed to be the final resting place of the gods and the center of Creation from which all life flew.“
- Area description
The xel’naga seed the universe with life from Ulnar
Ulnar served as the temple from which the xel’naga seeded the universe with life. It was located between dimensions, and served as a portal to the Void. After they had finished, the xel’naga rested within the temple, but not before creating an artifact known as the Keystone. The Keystone was designed to find its way into the hands of the ascended host races, races that would naturally become gain both purity of form and purity of essence, and guide them to Ulnar. It would then release the energy it had stored, awakening the xel’naga. The elders among them would give their essence to the chosen races, and they would ascend as the new xel’naga.
This plan went awry when Amon and his followers started to manipulate the Infinite Cycle to their own ends, and personally took a hand in uplifting the protoss and zerg. The creation of the Khala awakened the xel’naga in Ulnar, who fought him and pushed him back into the Void, but at a high cost. The few that remained returned to their slumber. Ulnar took on mythical proportions within protoss culture as a realm of myth; the place from which all life flew.
Hier können wir relative gut erkennen, wie Ulnar, als Bastion, änlich der Pandamoniumfestung in Diablo und dem wirbelnden Nebel in WoW als Verbindung zwischen den Realitäten und Dimensionen schwebt.
In Ulnar selbst, liegt die Kammer des Aufstiegs.
In ihr wird es den würdigen Wesen erlaubt, ihre Sphäre zu verlassen und selbst zu Xel´Naga zu werden.
Wir können also davon ausgehen, das sich hier die Energien befinden, welche an den Singularitätsstein oder Weltenstein gebunden sind.
End War
Upon Amon’s return to the material universe, he entered Ulnar and killed the xel’naga slumbering there. Sarah Kerrigan would send her Zerg Swarm to the temple only to find Amon’s hybrid inside. She and her broods would battle them for weeks.
Arrival at Ulnar
The Daelaam would arrive on Ulnar after discovering the location locked in the Keystone. Upon arriving they attempted to activate the celestial locks sealing the main entryway, but the Tal’darim and Moebius Corps attempted to stop them. The Daelaam broke through, and Hierarch Artanis entered the temple. He met with Kerrigan, and the two fought through Amon’s forces and the xel’naga constructs in order to discover the history of the xel’naga and the Infinite Cycle. However, when they arrived at the Chamber of Ascension, they found the xel’naga dead. Amon sprung his trap and opened a portal to the void within Ulnar. The combined forces of the zerg and Daelaam destroyed the void crystals powering the portal and sealed it.
A portal to the Void opened by Ulnar
In 2508, Kerrigan gathered her allies for an attack on Amon directly in the Void. Ulnar opened itself up as a massive portal, allowing their capital ships to attack Amon in his own realm.
Um es „kurz“ zu Fassen 
Ulnar und sitz der Xel´Naga, liegt zwischen den Dimensionen der realen Welt und der Leere.
Die Leere selbst kann von der realen Ebene nicht einfach so direckt betreten werden, was anders herum genauso gilt.
Dennoch verwenden viele die Energien der Leere (eigentlich alle Rassen).
Auf der anderen Seite sehen wir dahingehend z.b. in WoW die die Fürsten der Leere aber auch ihre eigenen Schöpfungen, die „alten Götter“ einsetzen und es auch andere Fraktionen gibt, welche einst aus dieser Dimension stammten und teils versuchen die reale Ebenen zu manipulieren.