Im totally captivated by this idea (sorry, late to the party) and have a couple ideas.
What if the ancient gods banished the insids there and then sealed off the realm? Say, it was the only 'elsewhere' safe enough that was also uninhabited by living souls to banish them. I say living souls because it could have been a go-between for the dead. They go there before they move on to where ever they go on their final journey, but since the gods sealed it off, the dead are stuck there in a sort of stasis.
The only way in is through death, but there's no way out now.
The djed storm of 512 weakened the veil but didn't entirely cause a rift (or maybe an earlier catastrophic even), and the insids have discovered that through magic they can reach the living realm and have begun harvesting the souls of dead mages trapped there and enslave them for that purpose; to further weaken the veil and learn how to better traverse it fully. Still, though, only through death (the more the violent or emotionally charged the death is easier, the manipulation) can the insids travel. Plagues, murders, suicides all draw the magic of the enslaved mages and thus the attention of the insids.
Maybe even have lore for a type of magic with a potential to allow a living mage to communicate, if not directly travel to, the realm. Maybe by a blood sacrifice and a longwinded incantation, one can walk the border or even pass through the weakened area and into the domain itself. That could make it for PC's to somehow explore the realm. Strict rules and guidelines can be presented to keep every tom, dick, and harry from continually trying to. Maybe even have a type of gnosis or mark given by the insids that allows the marked to approach the realm, the more times they are marked, the better the communication becomes before finally being able to travel the realm as you please.
Eh, just my imagination running away with me, but still, I love the idea!
What if the ancient gods banished the insids there and then sealed off the realm? Say, it was the only 'elsewhere' safe enough that was also uninhabited by living souls to banish them. I say living souls because it could have been a go-between for the dead. They go there before they move on to where ever they go on their final journey, but since the gods sealed it off, the dead are stuck there in a sort of stasis.
The only way in is through death, but there's no way out now.
The djed storm of 512 weakened the veil but didn't entirely cause a rift (or maybe an earlier catastrophic even), and the insids have discovered that through magic they can reach the living realm and have begun harvesting the souls of dead mages trapped there and enslave them for that purpose; to further weaken the veil and learn how to better traverse it fully. Still, though, only through death (the more the violent or emotionally charged the death is easier, the manipulation) can the insids travel. Plagues, murders, suicides all draw the magic of the enslaved mages and thus the attention of the insids.
Maybe even have lore for a type of magic with a potential to allow a living mage to communicate, if not directly travel to, the realm. Maybe by a blood sacrifice and a longwinded incantation, one can walk the border or even pass through the weakened area and into the domain itself. That could make it for PC's to somehow explore the realm. Strict rules and guidelines can be presented to keep every tom, dick, and harry from continually trying to. Maybe even have a type of gnosis or mark given by the insids that allows the marked to approach the realm, the more times they are marked, the better the communication becomes before finally being able to travel the realm as you please.
Eh, just my imagination running away with me, but still, I love the idea!