London (CNN) -- Plans for what promises to be London's most spectacular underground tourist attraction have been revealed: the $268 million transformation of a series of mile-long World War II tunnels into a dazzling, immersive experience.

Once so clandestine that they were once protected by the UK's Official Secrets Act, the former spy tunnels will be refurbished by a team of architects including those responsible for Singapore's Gardens of the Bay and Battersea Power Station, if the project gets approval this autumn.

The London Tunnels is a new multi-million dollar project that could become the British capital's most exciting underground tourist destination to date. Credit: DBOX/The London Tunnels

The Kingsway Exchange Tunnels, about 40 metres below Chancery Lane tube station in High Holborn, were built in the 1940s to protect Londoners from the bombings of World War II.

Kingsway Exchange Tunnels: The Kingsway Exchange Tunnels, photographed here in 1952, are a series of kilometre-and-a-half-long tunnels located under Chancery Lane tube station.
Credit: BT Media Image Library/Getty Images/Courtesy of The London Tunnels

That was the last time they were open to the public. Its next wartime role was to house the secretive Directorate of Special Operations, a branch of MI6 that inspired James Bond's Q division.

From telephone exchange to direct line

Later they were expanded to become the Kingsway Telephone Exchange, which in the 50s served as an internal communications center during the Cold War. It even housed the hotline connecting the leaders of the United States and the USSR.

World War II Shelter: This photo shows tunnels under construction in the early 1940s as a refuge for Londoners during the height of Germany's aerial bombing campaign against Britain.
Credit: BT Media Image Library/Getty Images/Courtesy The London Tunnels

The plant housed a dense network of 5,000 trunk cables and a busy community of 200 workers who manned the telephone lines.

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In the 1980s, British Telecom took over the facilities and created the world's deepest licensed bar for use by government staff, complete with a games room with pool tables and a tropical fish tank – the height of 1980s luxury.

Operations Center under Holborn: After a period as the headquarters of the top-secret Special Operations Executive, the tunnels became the headquarters of the Kingsway Telephone Exchange. Credit: BT Media Image Library/Getty Images/Courtesy of The London Tunnels

The telephone exchange technology became obsolete by the end of the decade and was dismantled. But now fund manager Angus Murray, CEO of The London Tunnels, wants to bring the tunnel's story to life for visitors with immersive high-resolution displays, interactive structures, scent technology and hundreds of precision speakers.

No expense will be spared when it comes to immersive magic. Credit: DBOX/The London Tunnels

Underground London

"The history of the tunnels, their scale and their location between London's Holborn and the historic Square Mile could make these tunnels one of London's most popular tourist destinations," Murray said in a statement.

The plan is to invest 140 million pounds ($170.5 million) in the restoration works and another 80 million pounds ($97 million) in all the extras.

The new project aims to bring the history of the tunnels to life through state-of-the-art technology and interactive exhibitions.
Credit: BT Media Image Library/Getty Images/Courtesy The London Tunnels

With Wilkinson-Eyre architects on board, they have a stellar team for this ambitious project, which far exceeds any other offering in the city. Today, London's most developed permanent underground tourist attraction is the Churchill War Rooms, located just 3.5 metres underground and a fraction of the 8,000 square metres occupied by the Kingsway Exchange Tunnels.

The tunnels in 1968, as a communications center. Credit: BT Media Image Library/Getty Images/Courtesy The London Tunnels

The London Underground also regularly organises guided tours of the city's abandoned tube stations and tunnels called Hidden London. These tours are always very popular and saturated, and tickets sell out as soon as they become available.

The tunnels were used until the late 1980s, when telephone technology became obsolete. Credit: BT Media Image Library/Getty Images/Courtesy The London Tunnels

However, they remain the best chance of an underground adventure for a few years, as the London tunnels project, if it goes ahead, will not welcome its first visitors until 2027. But everything indicates that the wait will be worth it.