With 775 rooms, Buckingham Palace is bound to contain a host of hidden nooks and crannies, known only to the Royal family and their closest confidantes.
Members of the public have now been given a glimpse of one such little-known secret, as the Palace invites cameras to take a peek behind a false door used by the Queen.
The door appears to be a cabinet standing against a wall, but this gives way to allow the Queen to slip from her private apartments into the White Drawing Room where she can receive guests.
The false door is pointed out to paying visitors who take part in summer tours of the palace, but is now there for the whole world to see thanks to a project which invites the public into the Palace for a "virtual reality experience".
Cameras have been allowed to film in seven of the state rooms, with the footage assembled to give a walking tour through the halls.Produced by Google, it is designed to be viewed on a mobile phone.
As viewers are taken on a tour by Vice Admiral Tony Johnstone-Burt, Master of the Household, they will be able to move their screens to look around the rooms from floor to ceiling, just as they would in real life.
The tour will move from the Grand Entrance Hall, up the John Nash staircase to the Green Drawing Room, where guests at the wedding of theDuke and Duchess of Cambridge were entertained by a harpist.
The virtual tour then encompasses the Throne Room, the Picture Gallery - which is home to works by Rembrandt and Rubens - and the Ballroom, with Vice Adml Johnstone-Burt showing viewers exactly where the Queen sits.
"As you can imagine, the atmosphere is electric," he says on the video. "Exactly where I'm standing now is where the Queen will sit at the top table, where she can see me and eyeball me very clearly if anything is going wrong.
"You can imagine there are over 200 people in this room, and the tables are groaning with silver and gold: more than 5,500 pieces of silver, over 2,000 pieces of cutlery and over 1,000 Georgian glasses.
We've got about 80 of my staff serving four courses, five types of wine, at the end of which, the finale is created by 12 pipers, walking around the ballroom and filling it with the glorious sound of bagpipes."Moving into the White Drawing Room, Anna Reynolds, curator at the Royal Collection Trust, points out the hidden doorway and opens it for the benefit of viewers. "The Queen can suddenly appear in this room," she says.
"If you look at this wall, you can see the fireplace and either side you see cabinets with porcelain and candelabra on top.
But the cabinet on the left actually opens and it reveals the secret door - it's very heavy - and that's where the Queen comes in from her private apartments when she's meeting guests here."
The tour was created using 16 cameras - known as a Jump camera rig - placed in a circle that filmed every aspect of the State Rooms.
Google has undertaken similar projects, which it describes as an "indoor Streetview", that took visitors inside the British Museum, Royal Shakespeare Company and galleries around the UK.
The public can take the virtual tour by logging on to the British Monarchy YouTube Channel with a smartphone.