What it’s like inside the secret World War II tunnels set to become a huge new tourist attraction

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London (CNN) — From Narnia to Alice in Wonderland, Britain’s best adventures begin with hidden doors or secret tunnels — and this is a tale with both.

Behind an unmarked blue door in London’s Chancery Lane, the historic legal district where Charles Dickens once worked as a clerk, CNN puts on a hard hat and high-viz as we embark on an exclusive hour-long tour 30 meters below ground (nearly 100 feet).

We’re here to explore a mile-long series of tunnels so clandestine that until 2007 they were protected by the UK’s Official Secrets Act.

There’s a literary connection here too, as this subterranean warren is the real-life inspiration for James Bond’s Q Branch — but that’s just one chapter in these tunnels’ storied history.

The next, if our tour guide and London Tunnels CEO Angus Murray’s vision is realized, is to become one of the world’s most audacious new tourist attractions.

“This is going to be a massive space, and it’s that impression of ‘wow!’ that makes a difference,” says Murray as we roam the 8,000-square-meter labyrinth that’s set for a $149 million transformation.

It will be part museum, part memorial, part art gallery, part cultural hub and — perhaps for many the biggest hook — home to the world’s deepest licensed bar.

The team for this mammoth design project includes Wilkinson-Eyre, the architects behind Singapore’s Gardens by the Bay and London’s Battersea Power Station.

World War II shelter

“You’re probably one of maybe 100-plus people who’ve been down here outside the Secrets Act,” Murray tells our small huddle of investors and media guests.

The space was constructed in 1940 and 1942 as a deep-level air raid shelter “built by hand by the British to save Britain and Europe against Nazi Germany,” he explains.

It was designed as two parallel “streets” running underneath the Northern and Central tube lines, more than 365 meters long and five meters wide (1,200 feet by 16 feet 6 inches).

It was one of eight such shelters built by the UK government during World War II in response to Germany’s Blitz bombing campaign that claimed the lives of around 30,000 people in London alone.

Built in just 18 months, it was intended to connect up to the tube station above, but Germany’s invasion strategy switched eastward to Russia and it was never put to use.

The Blitz had a “catastrophic effect” on generations of London families, says Murray, and their sacrifice will be memorialized in the History and Heritage section of the upcoming London Tunnels attraction.

Cold War cave

The tunnels’ next wartime role was as the home of Britain’s top-secret Special Operations Executive, an offshoot of MI6.

Ian Fleming, author of the James Bond novels, worked here in 1944 as a liaison officer for the British Navy.

“We have a partnership with the Military Intelligence Museum, the official museum of the armed services,” says Murray. Its base is currently in Shefford, a small town 90 minutes north of London, but the plan is for the museum to move inside the tunnels officially.

In 1949, the tunnels’ era as a communications hub began. They were taken over by the General Post Office, which at that time was responsible for telephones as well as the postal system.

The space was expanded with a series of “avenues” leading off the main streets, making this a unique underground environment — and this expansion would also open up the route for London Tunnels one day securing planning approval, explains Murray.

Its new role was as the Kingsway Telephone Exchange, which in the 1950s and 1960s served as an internal communications exchange during the Cold War.

It even hosted the “hot line” that directly connected the leaders of the United States and the USSR — and was put to use during the Cuban Missile Crisis of 1962.

The exchange was home to a heaving network of 5,000 trunk cables and a busy community of 200 workers manning the phone lines.

This British Pathé news reel from 1968 shows it as a hive of activity, with the industrious worker bees handling two million calls a week.

It’s from this period that most of the fascinating paraphernalia down in the tunnels dates from: ginormous generators, hulking machines with mysterious dials and levers and oh-so-many wires and switches.

“Anything you think is interesting, we’ll think is interesting and we’d keep it,” says Murray.

They’ll all be artifacts for visitors to digest in the planned History and Heritage section.

Hotline bling

British Telecom took over the site in the 1980s, creating the world’s deepest licensed bar for use by the government staff, complete with a games room containing snooker tables and a tropical fish tank — the height of 1980s luxury.

The technology behind the telephone center became obsolete by the end of the decade and was decommissioned.

Curios remain from this time also. It’s a time capsule of late 20th-century beige office fixtures, with a surrealist element added by one long room filled with doors that lead nowhere other than the bare tunnel behind.

The centerpiece of the space is the bar, which is set to be reborn on a grand scale, with renderings showing a warmly glowing curved space making the most of the tunnels’ unique design.

There should be capacity for a couple of hundred thirsty punters taking a break between areas to refuel and record the moment for social media.

Murray hopes that the glitzed-up tunnels will eventually pull in three million visitors a year, with the Arts and Culture section a key part of the appeal for repeat visitors.

While some parts of the London Tunnels maze will be retained as a cornucopia of fascinating obsolete thingamajigs, others are a huge blank canvas.

These will be used for rotating art exhibitions, interactive structures and spectacular immersive displays using digital screens, projectors, scent-emitting technology and pinpoint speakers.

Murray shows us a 26-meter-high, five-meter diameter construction shaft which can add depth and variety to the exhibitions. “You’re not just walking through tunnel after tunnel,” he says.

It’s all “easily interchangeable,” he says. “These could be museums full of modern art, like your MOCA, your teamLab in Tokyo, your Italian Luminaire, and you’ve got three big sections of it, each taking about 15 minutes.”

The London Tunnels plan is to “start construction at some point in the third quarter of next year,” says Murray, and the team hopes to open to the public in the first half of 2028.

Three million visitors a year is an ambitious target — that would put it on a par with the National Gallery and make it a bigger hit than the Tower of London.

The deep-level tunnels do however have one powerful sell that should help it pull in UK visitors year-round: It’s somewhere to go when it’s raining.

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