Perhaps the most famous of all cryptozoological mysteries, the Loch Ness Monster (or 'Nessie') is a large aquatic creature said to live in the depths of Loch Ness in the Scottish Highlands.
While witness descriptions of the creature vary wildly, common traits include a long, serpent-like neck and multiple dark humps protruding from the water. In general, the Loch Ness Monster has often been likened to a plesiosaur - a type of marine reptile that went extinct millions of years ago.
A model of the creature found in a pond near the Loch Ness Exhibition Center in Drumnadrochit on the north-west side of the loch also reflects this stereotypical depiction.
Sightings of a creature in Loch Ness and the surrounding area date back 1,500 years to the time of Saint Columba who, it is claimed, encountered the beast in the nearby River Ness in 565 A.D after telling one of his followers to swim across.
The story goes that Columba made the sign of the cross and said "Go no further, do not touch the man, go back at once!" which prompted the creature to retreat.
Other Famous Historical Sightings
The legend of the monster didn't really gain traction until the 1930s when eyewitness accounts of something lurking in the loch began to make local headline news.
On April 15th, 1933, Aldie Mackay and her husband famously reported seeing a large whale-like creature in the water while driving along the A82. The Inverness Courier
wrote at the time:"The creature disported itself, rolling and plunging for fully a minute, its body resembling that of a whale, and the water cascading and churning like a simmering cauldron. Soon, however, it disappeared in a boiling mass of foam. Both onlookers confessed that there was something uncanny about the whole thing, for they realised that here was no ordinary denizen of the depths, because, apart from its enormous size, the beast, in taking the final plunge, sent out waves that were big enough to have been caused by a passing steamer."
Later that same year on July 22nd, George Spicer and his wife had also been driving next to the loch when they encountered a bizarre creature crossing the road in front of their car.
Measuring 4ft high and 25ft long, the beast was described by Spicer as "the nearest approach to a dragon or pre-historic animal that I have ever seen in my life".
Before long, stories of the monster came thick and fast, kick-starting the modern Loch Ness Monster phenomenon and securing its place in the annals of history.
Nessie in the 21st-Century
Almost 100 years on from those early 20th-Century sightings, the monster remains a major tourist attraction with people from across the world flocking to the Highlands every year for a chance to glance across the surface of the loch.
Sightings can and do still occur, though most of these turn out to have conventional explanations.
Efforts to scour the loch with scientific equipment such as sonar have generally come up empty and to date no definitive evidence of the monster has ever been found.
Loch Ness is certainly large (and deep) - it contains more water than all the lakes in England and Wales combined. Even so, if there really has been a large, unknown creature living in its depths all this time, it stands to reason that there would need to be a viable population of them.
If the creature is a plesiosaur - as often depicted - then it would need to come up for air on a regular basis, meaning that we would expect to see a veritable forest of long necks protruding from the water all the time. (Not to mention the fact that plesiosaurs went extinct long ago.)
More feasible suggestions include the possibility that the phenomenon can be explained by sightings of a large fish (such as a greenland shark or catfish) or a huge eel (of which there are believed to be many in the loch). Other large animals could potentially make their way into the loch through the River Ness or Caledonian Canal, but these waterways are limited in size and the canal has multiple locks.
Ultimately, it is perhaps unlikely that one explanation can account for all known sightings of the monster.