While many of us witness creepy things every now and then, most of these cases usually get solved - much to everyone's relief.
However, when an answer is not found that's when the real thinking comes into play.
Back in 2015, photographs of glowing lights in a New Orleans hospital that had been closed for some eight years spooked much of the internet.
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Onlookers were left very unsettled after realizing the hospital had been shut since Hurricane Katrina hit in 2005, but there appeared to be some activity inside.
The light, which appeared to be a small Christmas tree, was first reported by Mike Arbon.
Facebook user Lisa Walley Staggs posted pics of the lights to the social media site and they quickly went viral.
"For those few of you who may not know... I work at an inner city New Orleans hospital that happens to be situated directly across from Charity hospital," she wrote.
"Charity hospital has been closed, its windows darkened, since hurricane Katrina, and is a gloomy and dreary sight on the best of days... at night it's down-right scary. Until tonight.
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"See, I park on the roof of my parking garage, and tonight as I was leaving work, I glanced over at the forgotten building, only to see the lights of a tiny Christmas tree! I wish the pictures did it justice. I don't know how it's lit. I don't know how it's even in there, but it made me smile just a little bit tonight!"
Many commented on the photo and linked it to paranormal activity, with one user writing: "Woah... is somebody living in there? What in the world? That kinda makes it creepier to me...like are ghosts having xmas up in there?"
A second user speculated: "Someone is taking credit for sneaking in and putting a tree in this room, can't personally confirm... photo of the outside of this room is going viral and people think these lights are a ghost Christmas tree."
As the photographs blew up on the internet, the police got involved to try and solve the case.
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Police officers told WWL-TV at the time that someone broke into the closed hospital and wrapped two-by-four wooden boards in lights and put them by the window.
“We are treating this as a break-in,” said Leslie Capo, from the Louisiana State University Health Sciences Centre.
However, officials were never able to arrest or pinpoint an individual to the apparent break-in - making it still a mystery to this very day.