Well, it all depends on what you believe but there IS a wide section of people who would agree that such a realm is real. Some would call it the 5th dimension (probably wrong, just saying), Astral realm, Otherworld etc. Some people think it's the "place" our essence goes while we're asleep, under deep meditation, astral projection and or powerful hallucinogens such as ayahuasca or peyote. Some would say that these are all different places, some, names for the same thing, and some would say they don't exist at all, and I personally believe that it depends on what you, yourself believe, as being shut down to a possibility may shut down the possibility in your personal reality (but again, it may be opened again).
Insofar as the elemental entities and archangels, as far as I know/believe they work on our plane as well, and aren't limited the same way we are.