Forget Area 51, the most terrifying alien conspiracy theories focus on a US military base so secret that its existence hasn't even been officially confirmed - Dulce Base.
The mysterious base is an underground facility in the middle of the New Mexico desert, said to be manned by aliens who carry out extreme experiments on abductees, including the creation of freakish extra-terrestrial-human hybrids.
Commander X, real name Milton William Cooper, wrote in his 1990 book The Ultimate Deception the lower levels of the maze-like base were home to tormented abductees who were never returned, as well as the freakish results of splicing human DNA to make horrible new hybrids.
He claimed to have testimony from a man who worked at the base who said that the huge underground facility stretched for miles down long tunnels connected by a high-speed shuttle system.
Cooper wrote. “There are at least seven different levels at Dulce, with Level Six known as ‘Nightmare Hall’. This level is used for most of the experimentation by the Greys.”
He added that one witness who had been “working in a slave camp under the spell of the Greys” was able to get a closer look at what was going on down there after mind-control “wore off”.
He apparently said: “I witnessed multi-legged ‘humans’ that looked half human/half octopus. Also Reptilians, and furry creatures that had hands like humans and cry like babies. It mimics human words… also huge mixtures of Lizard-humans in cages.
“There were also compartments of winged creatures, giants upwards of seven feet tall, and beings that were half-human, half bird-like.
“One level below this can be found row after row of humans who have been abducted and never returned to the surface. They are being held in suspended animation in cold storage units.”
But Cooper and his escaped slave source aren’t the only ones who have spoken out about this mysterious so-called alien hub. Its apparent existence has been detailed in outlandish UFO truther books, and mysterious Q&A sessions with whistleblowing former employees who gave up their secrets on their deathbeds - or so they claim.
A 2009 forum on AlienHub.com, titled, 'A terminally ill Thomas Edwin Castello speaks out', relayed answers about the base from a man who claimed to be a security guard who worked there decades prior.
Unsurprisingly, a lot of the questions centred on whether the aliens had sex, but the mysterious poster did provide some other insightful claims.
These included that he recalled the extraterrestrials relied on a strange liquid for sustenance; that he wasn’t sure if they washed themselves to keep clean because he didn't have access to their “private chambers”; and that they were scared of guns.
However, Cooper claimed that attempts by US Special Forces to wrangle back control had left 66 men dead after a particularly bloody fight between soldiers and aliens, known as 'Greys'.