The interdimensional UFO hypothesis (IUH)

 https://en.wikipedia.org/wiki/Interdimensional_UFO_hypothesis 

https://en.wikipedia.org/wiki/Cryptoterrestrial_hypothesis#UFO_reports_as_hidden_terrestrials 

If one sees a creature of almost any size and shape that seems to emerge from an interdimensional portal or doorway, who would believe them, let alone be able to prove it?

https://www.reddit.com/r/Otherworldpod/comments/1uq5430/i_saw_an_interdimensional_being_open_a_portal_in/ 

Yet, there are several myths and even legends about strange beings and creatures throughout history.

https://en.wikipedia.org/wiki/Interdimensional_UFO_hypothesis#Hynek_and_Vallee

https://en.wikipedia.org/wiki/Time-traveler_UFO_hypothesis 

Even if something very peculiar was recorded on a bunch of Flock cameras, the official explanation might be something like, it was just a flock of seagulls. 

https://therabbitportal.blogspot.com/search?q=Interdimensional+Doorways  

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George R. R Martin's Failed 1992 Multiverse "Doorways" television pilot

 https://www.looper.com/1304414/george-r-r-martins-failed-1992-multiverse-show-doorways-deserves-reboot/ 

The potential is still there, because of CGI and AI. A revamped TV pilot could use the original actors, plus any new actors and characters. 

https://georgerrmartin.com/notablog/2023/12/13/a-blast-from-my-past/ 

George RRM could do a total update, expanding upon his original concept.

https://www.ranker.com/list/doorways-lost-george-rr-martin-tv-pilot/shamus-kelley

https://www.businessinsider.com/george-rr-martin-doorways-tv-show-before-game-of-thrones-2015-11 

https://georgerrmartin.com/notablog/2010/07/24/doorways-coming-in-november 

https://ultimatepopculture.fandom.com/wiki/Interdimensional_being

Not just in Sci-Fi stories, symbolic everyday portals can be perceived.

https://www.tom-cox.com/the-20-best-interdimensional-portals-i-have-photographed-on-walks-in-the-british-countryside/ 

https://therabbitportal.blogspot.com/search?q=Interdimensional+Doorways 

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Interdimensional Doorways

 https://www.reddit.com/r/TopCharacterTropes/comments/1qu9g16/interdimensional_doors/ 

https://vocal.media/futurism/beyond-the-veil-do-portals-to-other-realities-exist

https://tvtropes.org/pmwiki/pmwiki.php/Main/PortalDoor 

https://marvelcinematicuniverse.fandom.com/wiki/Inter-Dimensional_Portal 

https://ultimatepopculture.fandom.com/wiki/Interdimensional_being

https://dexterslab.fandom.com/wiki/Inter-Dimensional_Doorway 

https://robertscheer.net/aramu-muru-portal 

https://georgerrmartin.com/notablog/2023/12/13/a-blast-from-my-past DOORWAYS

https://www.dictionary.com/browse/interdimensional and Inter-dimensional 

https://worldbuilding.stackexchange.com/questions/166651/what-s-the-difference-between-inter-dimensional-inter-universal-and-extra-dime 

https://therabbitportal.blogspot.com/search?q=Interdimensional+Doorways