LONDON.- There’s a locked door on the eastbound platform of the Chancery Lane station of the London Underground. The door is unassuming, sturdy and white.

Behind it is a wide set of stairs leading to a roughly mile-long maze of tunnels built in the 1940s that were first intended to serve as a World War II shelter and later used for espionage, the storage of 400 tons of government documents and telecom services.

Welcome to the Kingsway Exchange tunnels, set roughly 100 feet below street level in the center of London, sprawling beneath the Underground’s Central Line. Soon they could enter a new chapter: Angus Murray, the owner of the complex, who bought the tunnels last summer, has applied for planning permission to local authorities together with architecture firm WilkinsonEyre to turn the tunnels into a tourist destination that could handle millions of people a year.

Murray’s London Tunnels is planning to invest a total of 220 million pounds (about $275 million) on restoring and preserving the tunnels, as well as adding technology for art installations and other attractions. Murray hopes to open the complex in 2027, and said that it would be able to host temporary art exhibitions, fashion shows and more.

At the moment, entering the tunnels requires riding a small elevator tucked behind a side door in an alleyway off a wide street in central London. (Visitors to the attraction would use a different, bigger entrance, Murray said.)

When the elevator doors open, you step into a World War II-era tunnel — one of 10 civilian shelters proposed by the British government after the beginning of the Blitz, the eight-month bombing of London by the Germans that started in September 1940. The tunnels were never used as shelters. By the time they were completed in 1942, the Blitz was over.

During the Cold War, the British government instructed its telephone department, which later became British Telecom, to set up a secret communications system in the tunnels that could survive a nuclear attack. The famous hotline between the Kremlin and the White House ran through the complex, according to the project’s website. Some of the phone exchange’s equipment in the tunnels still survives today, even though it hasn’t been used since at least the 1980s.

“The idea was that it would provide a degree of protection,” said Martin Dixon, a trustee for Subterranea Britannica, a charity that documents and tries to preserve underground spaces.

“If the Cold War had turned into something more serious, it would have allowed communications on some level to continue,” said Dixon, who joined Subterranea Britannica about 40 years ago.

The tunnels under the Chancery Lane station of the tube are more than 1 mile long and in some places have a diameter of almost 25 feet. Those dimensions make them among the largest sets of tunnels built for people in a metropolitan city, Murray said.

“They have a fascinating history,” he said.

For a group of post office and telecoms workers in the decades after World War II, the tunnel complex became a workplace, some aspects of which have survived. In one room, the stuffy smell of an old carpet is inescapable. Another still holds the remnants of a canteen. Yet another has fake windows framing images of nature as decorations. There are still offices, as well as rooms where workers could spend the night.

Some parts of the tunnels are lined with fake walls and doors with nothing behind them. The effect is not unlike watching a scene from the dystopian Apple TV+ show “Severance.”

A bar where postal workers could drink is also still there, and Murray said he hoped to revive it and make it London’s deepest underground bar.

The tunnels’ communication operation became obsolete in the 1980s, and in 2008, British Telecom put the tunnels up for sale. BT employees used to go down into the complex up until the 1990s to inspect for fire safety and other conditions. The tunnels were otherwise vacant.

Many details of the new attraction still need to be ironed out, but Murray said the cost of the experience would probably be in the same price range as that of other major tourist sites in London. (The Tower of London’s entry fee is about $40, and Westminster Abbey’s is about $36.)

Dixon said he was excited about the prospect of the Kingsway Exchange turning into an attraction — provided it is safe and the history is preserved.

“I’ve seen thousands of underground spaces, from the mundane to the spectacular,” he said.

The Kingsway Exchange is particularly interesting, he added, because of all the different functions it had. “It played its part in World War II, and was ready to play its part in the Cold War.”

This article originally appeared in The New York Times.