If you had a huge situation map like in one of those cop dramas, and you used it to map all of the weird phenomena that get reported from time to time, you would find that a lot of the dots were clustered in a few “high strangeness areas,” also known as “window areas”- the Bridgewater Triangle, the Burlington Triangle and others.
A lot of people have presented a lot of different explanations for window areas, but here's the problem. It isn't just that one or two phenomena cluster in a particular place, it's that all manner of weird phenomena cluster in the same places. The Bridgewater Triangle, for instance, gets more than its share of cattle mutilations, UFO sightings, black helicopters, Satanic cults, phantom hitch-hikers, thunderbirds and giant black snakes.
Why would UFOs, Bigfeet, Satanists, and giant black snakes all be interested in this one little area south of Boston? None of the standard explanations really seem to make a lot of sense. So here (in the spirit of Charles Fort) is what I propose:
Window areas are not really home to unusually large numbers of hairy hominids, nor are they especially attractive to alien visitors. They are simply “fey” places, places that are inherently weird and numinous. In these areas, things get really weird every now and then- weird in ways and on levels we can't even describe- and sometimes someone happens to be there to witness it. Because the human mind cannot directly represent this numinous strangeness, it translates it into whichever culturally appropriate mythological archetype springs up first in the unconscious mind of whoever happens to be there. To a medieval person, it might have been fairies. To a modern person, it could be UFOs instead.
This is the only explanation I can think of to account for window areas. Actually, I can think of other explanations but not interesting ones so I won't waste my time with them!