Portals
The portals that connect Shengdao with earth are older than any human civilization. They were created through sacrifices of the elders to save the species from the Cretaceous-Paleogene extinction. It needed a huge number of sacrifices to open up the rift to another dimension. Shengdao is a realm between the physical earth and the void, a world full of magic. It resembles earth quite significantly, with fauna and flora being very similar. The realm has different climatic zones, from tropical biomes to tundras, all connected via one giant landmass.
Elder Shiji-Long sacrifice their own magic, their life force, to open portals and keep them open. A lot of elders thus didn't reincarnate, since they saw it as their duty to uphold these portals to their new home world. There are elders who denied their responsibility to care for the magical transportation system and are unwilling to sacrifice themselves for anyone, even their decendants. These elders have been condemned and outcast, as they were too selfish to offer value to their descendants. No one knows if there are still some of these elders around today. Currently there isn't knowledge of when the last elder had sacrificed themselves for a portal or when that ritual has to be performed again. One thing is clear though, without magic, the portal connecting Shengdao and earth will eventually fade away.
Records show that there have been more than one portal in the past. The current portal arc had housed quite a few more. There are also old notes and scriptures that certain famous places on earth were used as portal arcs back in the distant past, which are now monuments of human interest.
Such places include 
stonehenge, the hanging gardens of Semiramis and a lot of others.
