The concept of portals - or doorways to other worlds - has been one of my favorite subjects. In fact, my newest released book (#3 of 3-book series), "Threshold," handles this exciting subject with nail-biting pace.
When I was recently on the Talking Story Power Hour show hosted by Chai Gallahun, we talked almost exclusively about the subject.
Portals are considered to be openings in which beings can come and go from one world to another.
Here's just some portal concepts -
If you ever wondered at the merciful design of creatures and humans, just consider the sleep state. When light gets low at end of day, melatonin is released to put you to sleep and forcing rest. Then, in deeper sleep stages, forcing paralysis so you don't act on the dreams that give you insight. Wow!