The Bair of Lacuna is the refuge Ceridwen created to protect Os-Gabella from the gods who wished to for her to submit to Nemed or destroy her (this was before she was suicidal). It was protected by many powerful runes that hid it even from the sight of the gods themselves and which prevented unwelcome souls from entering or existing from other planes. Although never openly stated, it is widely believed not to be an actual part of Erebus but a small pocket dimension tied to this plain and perhaps many more.
The secret room below the Sheaim palace where the Queen of Storms keeps Nemed prisoner and tortures him (and occasionally a few others) may actually be the Bair. If so, then it is at least tied to Erebus closely enough that echos of her victim's screams can be heard n the city.
Alexis and Flauros were raised in the Bair of Lacuna as Os-Gabella's adopted children. They were the only mortals admitted there in the Age of Dragons. This led Alexis, the elder sibling, to become terrified by the knowledge that she would be the first person to die there. Her adoptive mother took her to see the deaths of mortals in Erebus to show her it was no big deal (this was perhaps when she began to envy the ability of mortals to find rest rather than live forever), but Alexis decided she needed a closer inspection and so left the Bair on her own to murder an shepherd that lived nearby in hopes of seeing where his soul would go. In the Bair Alexis had access to the teachings of Ceridwen as well as the goddess's most powerful runes, allowing her to study ways of consuming the soul. In her second murder she used this knowledge to torture Lanthis, a young acolyte of Lugus, past the point of death without allowing his soul to escape to find rest. (This likely worked in a manner similar to that of the rune Samael used on Einion's wife on Valledia's orders in order to frame the Infernals for breaking the Compact.) Eventually she grew board with this and entered the circle of runes and performed a ritual that let her victim's soul escape, not to the Netherworld but into her body. The ritual did not make it possess her, but let her consume it. (The Eaters of Dreams and even Agares himself are known to use a similar or maybe even identical ritual. It probably started out the same but Alexis likely altered it.) I suspect that said Sheaim Archmage UU my actually be a high priest of the Emyrs. Ceridwen is known to have taught her disciples to use sorcery themselves rather than rely on divine miracles, so there is little difference between arcane and disciple in that faith.) During that last ritual Alexis's lips touched Lanthis's bleeding forehead, and she quickly developed a taste for blood. Lugus placed a curse upon her for her treatment of his beloved disciple, and both the bloodlust and curse carried over to those with whom Alexis shared the secret ritual (first her brother, and then a very small number of their followers). Drinking blood is not a necessary part of the ritual, but many vampires love to gorge themselves of the fluid anyway. The early vampires did not hunt often, as a single victim could easily sustain a vampire for 20 to 30 years (perhaps however long the victim could have lasted until a natural death). They may need more sustenance as they age, but more likely they just become more glutenous. Also, they want souls not only to stop their aging but to give them superhuman strength and rapid healing.
I do not believe that vengeance is possible for the sphere of Light, so the curse must have been an attempt to supplement her clearly deficient conscience. Sunlight is not fatal to vampires (except at levels high enough to cause a normal human life threatening sunburn, but it weakens them and is painful. In direct sunlight a vampire looses all his supernatural strengths but still possesses all natural human abilities. I suspect that strong light may cause them to feel just like their victims did when they destroyed their souls, but it does no real damage. Presumably a more guilty vampire would feel it worse, as more pain is needed to offset their more deadened natural conscience. Lugus is tough but merciful, so I'm sure a vampire that truly repents would have the curse lifted. That would probably go hand in hand with loosing all supernatural abilities though, including longevity, which may mean an ancient vampire could find salvation only in the next life but a young one may still have decades of natural moral life.
When Alexis and Flauros became vampires they began serving Aeron, God of Body, Strength, Cunning, Rage, Hate, Rape, and Murder. Os-Gabella hates Aeron more than anyone, and will never forgive him for his attempt to rape her. She sees Alexis and Flauros's actions as choosing to be the children of her rapist rather than hers. This is the ultimate betrayal. I think it is safe to say that the vampires are not welcome home.
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