Inside dark history of abandoned prison being turned into a HOTEL – with tunnels & terrifying dungeon called ‘The Hole’

The 33-acre fortress, known as the Citadel, sits on Dover's Western Height and is entered via a concrete bridge over a grassy dried-up moat.

Mr De Min hopes to create a globally recognised tourist attraction in its place, which could cost him anywhere from £200million to half a billion.

He is the first person to own the site since King George IV in 1808.

The Dutch-born entrepreneur told MailOnline: "This place has stood for 245-years, first as a foreboding fortress protecting the country and later as a place of incarceration.

"Teachers in Dover would point up to it and warn naughty children: 'If you don't behave you'll end up in there'.

"My hope is that, going forward, teachers will start pointing up and saying: 'If you're good, you may be lucky enough to work there."

The ambitious businessman said he wants his project to "inspire and innovate".

Some of the fortresses eldest parts date back to 1775 and saw Napoleon use it as a defence.

It later served as military barracks in the Crimean War and both World Wars.

In 1956 it was given to the HM Prison Service and became a Young Offenders Institution until 2002.

There's still a 1970s prison block with over 60 cells across three floors on the abandoned site and an anti-suicide net is still in place.

A swing hangs over the netting, and Mr De Min explained he was lowered 130-ft down into the on-site well.

He said: "I was hoisted down to fetch a sample of water to see how pure it was.

"There's a jar of the water in my office, it's crystal clear, perfect, and means we have our own water source which fits in with our sustainability ethos."

It was then used as an Immigration Detention Centre up until 2015.

The Citadel is made up of a whopping 54 buildings totally around 220,000 square feet.

Below lurks around 30,000 square feet of eerie tunnel networks.

Now, the atmospheric location is sometimes used as a film set, including an upcoming Marvel movie Kraven the Hunter starring Aaron Taylor-Johnson.

Mr De Min even landed himself a small role as an extra, playing an inmate.

Despite it's dark history, the entrepreneur is determined to forge an entirely new future - although it could take up to 25 years.

"What we're hoping to do is to install a stage complete with lighting and speakers for a Dragons' Den-style TV show, where budding entrepreneurs will pitch ideas for innovations in business and technology," he said.

"In front of the stage will sit five potential investors, all well-known billionaire businessman. I've had the greenlight from Sky TV to start production."

The creep basement cells will also be given a major re-vamp and turned into a state-of-the-art wine cellar with tasting experiences.

There may even be a posh cigar bar, for any aficionado's who enjoy an evening smoke.

They could sample a range of products while sipping on premium whiskey - as Mr De Min hope to install his own distillery too.

These plans are partly funded by police forces who rent out part of the site to train armed counter-terror squads.

Mr De Min also claimed a globally renowned events company is interested in creating a concert venue there.

He said: "They approached us with the idea, we can't give out too much information because we're under an NDA but we could easily do big numbers on it."

The businessman dubbed it "one of the most unique gig venues in the world".

But perhaps one of the biggest goals is to create a wellness retreat, offering guests "hyperbaric oxygen chambers, laser infused IV drips, cryogenic chambers and ice bath".

"It may take ten or 25-years to complete this project but I'm someone who lives for the future, I live by my visions," he added.

The 33-year-old also plans to build sustainable homes, create a biohacking lab, and open a restaurant in the "Secret Garden."

David aims to host Techfort, a hub for start-ups where they can pursue their ideas for sustainable technology.

Summer Raemason, News Reporter