Panorama investigator John Sweeney today reveals the sinister site where Tom Cruise's Scientology church has carved a message to aliens that can be seen from outer space.
The BBC reporter - who erupted in fury at a member of the weird sect during a 2007 programme - tells how he travelled deep into the New Mexico desert to see the Scientologists' "alien space cathedral".
The site is home to the buried texts of Scientology founder L Ron Hubbard and was built to withstand a nuclear holocaust.
Sweeney says in his new book Church of Fear - adapted here by BEN JACKSON - that the group collects tens of thousands of pounds from each member.
It even palms them off with two cheaply-made electronic gadgets for 100 times the cost of manufacture, according to one former Scientologist.
If you don't have a flying saucer, Trementina Base is not an easy place to get to.
But if you're a visitor from outer space, it's a doddle because the Church of Scientology has etched two vast interlinked circles on top of a mountain amid the desert scrub of New Mexico.
Each circle has a huge diamond shape inscribed inside as a sign to aliens.
Just dial up Mesa Huerfanita on Google Earth and you'll find a nearby mountain scarred by a long concrete strip with a short leg at the northern end pointing east. That's the loony church's private airport.
A zig-zag white line from the strip heads north. That's the church's private road. It leads to the two linked circles - invisible from the land below.
The spot is north of Roswell - a town linked to UFO sightings.
My mobile phone signal dies as soon as I turn off the freeway. This is harsh country like something from a John Wayne western.
The closest settlement, Trementina, is virtually a ghost town. But an old local gives me directions to Trementina Base: Take the dirt track, drive for 30 miles, then you'll find a gate.
My driver is Marc Headley, a former Scientologist who says he was "audited" - given spiritual counselling - by Tom Cruise, Hollywood superstar and leading church member.
Marc says he was also beaten up by the shadowy church's leader David Miscavige. The church denies both incidents.
After passing through a rocky gulch we come to a gate marked No Trespassing. Gingerly, we pass through and drive on.
Two more gates are marked No Trespassing. Trementina Gulch is the creepiest place I've ever been. We decide to turn back but try again after getting firmer directions.
We are seeking the space alien cathedral that ex-Scientologists say was built deep underground by the church in the 1980s at the cost of millions of dollars. Its vault houses the lectures of church founder L Ron Hubbard on gold discs locked in titanium caskets sealed with argon. The cathedral is H-bomb proof, protected by three 5,000lb stainless steel airlocks.
Experts say the weird signs on top of the mountain will guide Clears, (high-ranking Scientologists) returning from space to find Mr Hubbard's works after a nuclear Armageddon wipes out humanity.
Ex-Scientologist Chuck Beatty, of Pittsburgh, has said: "The whole purpose of putting these teachings in the vaults was so that in the event that everything gets wiped out, someone would be willing to locate them and they would still be there."
The cathedral must have been a huge project needing lots of labour, earth movers and boring gear plus tons of concrete and steel.
The light is fading. I have come 4,500 miles to find this thing, and it is looking like the worst wild goose chase ever.
But we turn one last corner and Marc and I are suddenly confronted by a massive steel gate, secured by a combination lock and guarded by two security cameras. I press an intercom button. A voice says "Hello" in what sounds like a Scandinavian accent. I announce that I'm John Sweeney and ask nicely for a tour. We are not invited in and the intercom simply spouts white noise. We drive back to civilisation, wondering what kind of religion builds a space alien cathedral underground.
The "Church of Fear" is not finished with us. We stop the night at a Best Western hotel in the small town of Las Vegas, New Mexico. At 1am Marc receives four mystery phone calls to his room.
Each time the caller hangs up as soon as Marc answers. Both our rooms were registered in my name. They got the wrong room. But still impressive, in a way, because I didn't book in advance and paid cash. Next day we drive back to Marc's home in Colorado, talking about the Church in which he spent his life from the age of six.
Marc's book Blown For Good: Inside the Dark Curtain of Scientology is the bible for Scientologists thinking of leaving the Church. Members often call him for advice.
Marc tells me: "I don't criticise Hubbard, I don't say it's all bad, I start with money and maths. For instance the E-meter (a device which the church uses to measure the static electric field around a person) costs $40 ($24) to make. The church sells them for $4,000 ($2,400). And everyone needs two in case one breaks down."
Marc says the church also rakes in a fortune charging members $50,000 ($30,000) a time to be made Clear - free of unwanted emotions or threats in the unconscious.
It strikes me that a church is not the right word for an organisation that places gold in a vault under the ground. In English we call that a bank.
