Standing at the mouth of the Humber estuary, between Hull and Grimsby, Bull Sands Fort was built in 1915 to bolster shore defences. Its developers hope it will be a place to bolster addicts' resolve to kick the hard drug habit.
Clients will stay at the fort for 30 days, going through the traditional 12-step recovery programme established by Alcoholics Anonymous. They may then go on to rehabilitation clinics and further counselling.
There will be space for 160 patients and a team of doctors, counsellors, psychiatrists and psychologists. The pounds 1m project recently received planning permission from East Riding of Yorkshire Council, and engineers are already drawing plans for a dramatic conversion.
"This will be for people who have tried other methods and failed to get rid of their addiction. It will be the end of the line," said Philip Ball, a trustee of drugs charity Streetwise which has bought the fort freehold. "A lot of shore-based clinics are very good but one thing they can't provide is a secure environment. There will often be a pub round the corner. That's not the case here. This is a retreat. It will be like going to a monastery."
Visiting the fort, three miles off Cleethorpes, is like entering a futuristic, almost nightmarish ghost ship. The only way to get there is by local fishing boat or in the Cleethorpes lifeboat. From a distance, the fort resembles a giant tank stranded by the high tide; it is 100ft high, built over four storeys, and planned like a vast drum with reinforced concrete. It weighs some 40,000 tons.
Inside, it is dank and unwelcoming. Floors are caked in four inches of bird dropings; railings rattle in the wind, and pigeons flap at the unexpected visitors. It is easy to see how the First World War gunners lived, for their kitchens are still recognisable and their metal spring beds are lined up in the old living quarters, littered with droppings and feathers. In what was the boiler room, a previous inhabitant has left a novel behind: The Secret Sanctuary. A bell tolls on top of the fort's highest mast.
At high tide, the Humber bubbles and swirls 20 feet deep around the base of the fort. Addicts will be taken to and from the fort by a trawler boat or tug, and a helipad will cater for emergency cases and to enable "celebrity" addicts to visit the clinic at short notice.
"It will not be easy to get off," said Mr Ball, referring to the fort. "With the tides, it will take 24 hours and any counsellor worth his salt should be able to persuade someone to change their mind within that time. Addiction can take a terrible grip, so it can require an equally strong solution."
Streetwise wants the centre to offer immediate assistance. "You can wait four years with some local authorities just to get an assessment for treatment. That's not a lot of good," said Mr Ball, whose son died at the age of 21 from heroin addiction - because, he says, a detox service was not immediately available. The new centre is to be named the Stephen Ball Alcohol and Narcotic Detox Sanctuary.
Nearby Grimsby is a town all too familiar with the problems that drugs can bring. The recent count of young deaths from drugs was three times the national average.
John Nawrockyi, deputy director of social services for North East Lincolnshire Council, said there would be local sympathy for the project. "Isolation can take a person away from the culture, and buy time for that person to change. But you have to be careful not to separate the person so much from the community that they can't cope with going back again."
Gary Barlow, of the Cleethorpes Inshore Lifeboat Service, added: "This is far enough off shore not to affect anybody. They're not exactly going to pop over into the town, are they?"