The first recorded sighting of a "monster" in Loch Ness was nearly 1,500 years ago. Apparently, a huge, ferocious beast leaped out of a lake near Iverness, Scotland, and ate a local farmer. Since then, the lore of Nessie has grown and grown.
A photograph, taken in 1934 by a London doctor, seemed to show a dinosaur-looking creature with a long neck emerging from the water, and it fueled the Nessie obsession.
Then a home movie shot in 1960 showed a family picnicking near the water, but the movie also shows a strange figure swimming nearby .
British intelligence analyzed the film and concluded it was probably "something animate."
Millions of people have peered into this forbidding water, in search of the truth. One-thousand visitors have reported unusual sightings.
One woman named Val who claims to have spotted Nessie said the creature she saw was "very dark gray. Shiny, obviously, because it was wet."
MIT professor Robert Rines was at a Scottish tea party in 1972 when he and the others spotted what they thought was the Loch Ness monster.
"It was a big tremendous thing. Like the back of an elephant," Rines said. "It came back, right in front of us and ... thuuup. Submerged!"
Rines, now 85, has returned to Loch Ness almost every summer since that first sighting, hoping to prove that he did see a monster.
Using sonar technology, he plumbed the vast, vast blackness of Loch Ness -- which is 750 feet deep, 23 miles long, 380 million years old -- and claimed he detected large, moving masses.
In 1975, he captured underwater photos of what appeared to be the body, flipper, neck and head of a large animal.
"This is probably a progenitor of something that should have been dead 65 million years ago," he said.
Since the 1980s, Rines' underwater sonar and photos have not picked up any trace of a creature. Rines' latest theory is that Nessie might now be dead, and he wants to comb the Loch's bottom for bones.
A recent video showed suspicious movement in the Loch. But that was actually me swimming in the inhospitable waters, demonstrating that it's easy to fake a sighting.
The water was just a few degrees above freezing the day I went in, and it was murky and dark. There aren't even many fish brave enough to live in here. So what sort of monster would choose to call Loch Ness home?
Some have speculated that Nessie might be a plesiosaur, a type of dinosaur that resembles other lake monsters spotted around the world, and looks a lot like Nessie.
Adrian Shine, head of the Loch Ness Project, has spent 30 years trying to prove Nessie doesn't exist.
"I don't happen to believe that Loch Ness is Jurassic Park. I think it's about the last place on earth a warm water marine reptile of the Jurassic era would actually want to live," Shine said.
Shine said certain natural phenomenon like boat wakes or unusual currents created when warm surface water meets the cold water below.
These kinds of currents can make a floating log look like it's swimming upwind, and create visual illusions, Shine said.
For science, eyewitnesses are not proof enough.
But for me, they're enough to keep my imagination running wild.
ABCNews' Jonann Brady contributed to this report.