Interrealm travel actually involves passing through the in-between – a vast network of passageways connecting all realms. only complete spirits can navigate the in-between as it is. mortals and lesser spirits must use rifts and gates to temporarily connect two portals of the in-between. if a mortal/lesser were to enter a rift, it is unknown what would happen to them. A theory is that the body and spirit would simply cease to exist.
or they would be doomed to wander, hopelessly lost in the endless maze of the in-between forever.
Rifts are the raw portals between realms. Most rifts are only one realm deep. (dawning – median, and median – sundered) except the Eye of the Abyss, it is the only known rift that connects all three realms. Mortals cannot just walk through a rift, a gate must be set to allow safe passage.
A rift key is an artifact allowing the safe travel through a rift without a gate, but the trip is one way and the key is destroyed upon use. still, the keys are very rare and valuable.
The Eye of the Abyss: Sundered/Median/Dawning
Sunia’s Hubris: Sundered/Median
The Great Ocean: Median/Dawning
many large cities in Syraad are connected via manmade rift gate to sundered undercities. these rifts are monitored and maintained by rift mages (wizards specializing in transrealm travel, teleportation, etc.)
Most dwarves no longer live in the sundered but their tunnels do criscross into the realm, and a few dwarven cities worldfall between the realms.