Everyone's heard of Area 51, right? The secretive US Air Force military base has been the subject of many conspiracy theories, most notably surrounding UFOs and aliens.
The site rose to new infamy a few years back when thousands of people showed up to storm the facility in a bid to uncover its mysteries.
But today we're turning our attention to a place a little closer to home - a site that's often referred to as the UK's answer to Area 51.
Now, you might think that with the UK being as small as it is, it would be pretty hard to keep anything of this magnitude under wraps - especially in the age of the internet.
But it turns out, nestled away in the English countryside is an elusive base that to this day has left people with more questions than answers.
And you can bet conspiracy theorists have their fair share of ideas on what goes on down there.
The place in question is RAF Rudloe Manor, formerly known as RAF Box.
Situated between the settlements of Box and Corsham in Wiltshire, the overground building appears as if it's any other English estate.
But beneath the bricks and mortar lays a complex and extensive network of tunnels and bunkers that were used for a number of purposes over the years.
During the Second World War, it was used by the RAF's operations group for various purposes, including filtering intelligence on enemy activity.
Rudloe Manor was also the former location of a civil defence division responsible for monitoring radiation hazards and nuclear risks at the height of the Cold War.
But for decades rumours circulated that there was another reason the estate was kept so firmly under wraps.
Theorists suggested that the UK's Area 51 was used to conduct research into UFOs and make contact with extraterrestrials.
Perhaps the most well known story is that it hides the remains of an alien spacecraft and its otherworldly crew.
This didn't come from thin air, either - the theory was first put forward by American writer Dorothy Kilgallon, who claimed that the crash unfolded in the 1940s.
She alleged that she was told about the incident by a high-ranking British official, although understandably they wished to remain anonymous.
Now, none of this has been confirmed, and the claim that Rudloe Manor was used for UFO investigations was continually denied by the Ministry of Defence (MOD).
However, as outlined by Sky History, this all changed in 2007 when declassified secret files released at the National Archives suggested that the site was in fact used for this purpose in the 1950s.
The outlet went on to point out that despite no longer being in active use by the MOD, the site is still fenced off and under strict guard.
And it's for this reason many people still believe there's far more to this story than meets the eye.
This is certainly true for folklore enthusiast Neil Cartwright, who told Sky History: "We all suspected this was happening at Rudloe Manor, but they operated as a clandestine organisation unregulated for decades, never held accountable to the British taxpayer.
"I’ll definitely be keeping an eye on this story in the coming years."