Disused Tube stations and tunnels are being opened to the public as part of London Transport Museum's Hidden London festival. Visitors can book tours of four locations that are usually off limits, including a decommissioned station that was used as a secret underground bunker by Winston Churchill during the Second Wolrd War.

Down Street station opened in March 1907 on what was then the Great Northern Piccadilly and Brompton Railway. It was never very busy as it lay between the more popular stations of Hyde Park Corner and Green Park. The station was permanently closed on 21 May 1932.

In early 1939, as war looked likely, it was turned into an underground bunker to protect vital government operations from bombing raids. The platform areas were bricked off and divided up into office, meeting rooms and dormitories. Although this shelter was chiefly used by the Railway Executive Committee, Sir Winston Churchill and his war cabinet used it while the Cabinet War Rooms were being prepared. Churchill apparently liked the bunker, affectionately referring to it as "The Barn". A bathtub with the inscription "WC" can still be seen in a disused bathroom.

Down Street tube station
A guide illuminates part of an old lift shaft inside the former Down Street underground station Dan Kitwood/Getty Images
down street tube station
A sign points the way out via the stairs in the disused Down Street underground station Peter Macdiarmid/Getty Images
Down Street tube station
A stairway inside the abandoned station Dan Kitwood/Getty Images
Down Street tube station
A London Transport Museum employee walks down stairs inside the decommissioned station Dan Kitwood/Getty Images
Down Street tube station
A member London Transport Museum staff walks down a tunnel Dan Kitwood/Getty Images
Down Street tube station
A visitor is silhouetted in a tunnel inside the disused station Dan Kitwood/Getty Images
Down Street tube station
A sign inside the disused station points to street level Dan Kitwood/Getty Images
Down Street tube station
A worker shines a torch to illuminate a sign inside the disused Down Street tube station Ben Stansall/AFP
down street tube station
A tunnel leading to the platforms is seen inside the disused Down Street station Peter Macdiarmid/Getty Images
down street tube station
A pedestrian tunnel inside the former Tube station Transport for London
down street tube station
Modern day signage displays platform information in the disused Down Street station Peter Macdiarmid/Getty Images
down street tube station
A worker walks along a tunnel in the former underground station Peter Macdiarmid/Getty Images
down street tube station
Stairs leading up from platform level are seen in the disused station Peter Macdiarmid/Getty Images
Down Street tube station
A security door between the tunnel and tracks inside the former station Dan Kitwood/Getty Images
Down Street tube station
A map hangs on a wall inside Down Street underground station Dan Kitwood/Getty Images
Down Street tube station
The station, designed by architect Leslie Green, has a red glazed terracotta facade Dan Kitwood/Getty Images
down street tube station
Second World War era lettering is seen in part of the disused Down Street underground station Peter Macdiarmid/Getty Images
down street tube station
A Second World War era sign points the way to the committee room Peter Macdiarmid/Getty Images
down street tube station
A derelict bathroom in part of the disused Down Street underground station is lit by torch light Peter Macdiarmid/Getty Images

Visitors will also be able to see a warren of tunnels underneath Clapham South station. Built during the height of the Blitz in 1941, after the loss of life at several improvised shelters in underground stations, this shelter provided sanctuary for 8,000 people. After the war, the space served as a temporary dormitory for immigrants from countries such as Jamaica.

The tunnels were rebranded as the Festival Hotel in 1951, providing cheap, temporary living spaces for visitors to the Festival of Britain. Clapham South deep-level shelter has over a mile of subterranean passageways.

Clapham Souths wartime renovation
A worker for Transport for London walks down a large shelter tunnel at Clapham South deep-level shelter Chris Ratcliffe/ Getty Images
Clapham Souths wartime renovation
A Transport for London worker walks through the recreation and games room at the Clapham South deep-level shelter Chris Ratcliffe/ Getty Images
Clapham Souths wartime renovation
Grafitti from soldiers and members of the public who took shelter during the Second World War is seen on the ceiling above bunk beds at Clapham South deep-level shelter Chris Ratcliffe/ Getty Images
Clapham Souths wartime renovation
Signs to shelters named after senior British naval officers at the Clapham South deep-level shelter Chris Ratcliffe/ Getty Images
Clapham Souths wartime renovation
Bunk beds at the Clapham South deep-level shelter Chris Ratcliffe/ Getty Images
Clapham Souths wartime renovation
An entrance to Clapham South deep-level shelter seen from street level Chris Ratcliffe/ Getty Images

London Transport Museum is also allowing people to explore a labyrinth of dark and disused passageways under Euston Station. Visitors will see vintage advertising poster fragments that have been concealed for more than 50 years.

Euston station
Visitors look at preserved vintage advertising poster fragments London Transport Museum
Euston station
A visitor explores a hidden tunnel at Euston London Transport Museum

The fourth venue being opened up as part of the Hidden London festival is London's first skyscraper, 55 Broadway. Considered radical and offensive when unveiled in 1929, this Grade I listed structure is now a marvel of Art Deco London. London Underground's former headquarters gives stunning rooftops views.

55 Broadway
55 Broadway, London's first skyscraper London Transport Museum
55 Broadway
Visitors admire the view from 55 Broadway London Transport Museum

Hidden London runs from 4 August to 11 September 2016, 24 November to 18 December 2016 and 11 January to 5 March 2017. For priority booking, sign up to London Transport Museum's newsletter by 23.59 on Monday 18 April 2016.

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