A Tube journey is the norm for millions of London commuters but the Prince of Wales and Duchess of Cornwall have only just taken their first joint trip on the Underground.
Charles and Camilla celebrated the 150th anniversary of the capital's transport network by touring a small part of it and visiting some stations on Wednesday.
The Prince and Duchess travelled by Tube riding for a few minutes just one stop from Farringdon to King's Cross on a Metropolitan line train.
The royal couple were given specially designed oyster cards celebrating the Tube's anniversary
Charles last travelled on the Tube network in April 1979 when he opened the first stage of the Jubilee line, while Camilla is thought to have used the London Underground (LU) in the past.
They both qualify for a Freedom Pass for the over-60s, but their oyster cards had £10 credit for the journey, which costs £2.10. The cards are expected to be retained by the Royal Collection.
In their carriage were senior LU and Transport for London staff and Charles and Camilla sat next to each other on the train bound for Uxbridge in west London, while most of their hosts stood.
The Prince and Duchess travelled along the route of the underground's first line which opened on 9 January 1863 and ran services between Paddington and Farringdon.
A brand new train was used for the journey, part of LU's new S-Stock trains, which are being introduced to 40% of the Tube network.
The walk-through, air-conditioned trains are built at the Bombardier facility in Derby, which Charles visited in February last year.
Although the train was empty, members of the public boarded at Farringdon along with the royals but a group of policemen standing further down the carriage meant commuters could not reach the heir to the throne and his wife.
Camilla sat opposite Metropolitan line manager Angela Back and speaking about the immaculate train said: "Very nice, very smart."
The short journey was to mark 150 years of London Underground
"Just one stop?" Charles asked Tube bosses when he and the Duchess arrived at King's Cross station after their three-minute trip from Farringdon.
Prior to boarding, Howard Collins, the Tube's chief operating officer, asked Charles if he would like to drive the train - as he did a year ago during the Bombardier factory visit.
"I will do as I'm told," Charles jokingly replied.
Spotting the media waiting on the same platform, he asked: "Are you all coming on the train?"
He asked Tube managing director Mike Brown whether Transport for London was able to recycle any parts from the old trains.
Brown said this was done as far as possible but there were problems with asbestos.
During the journey, TfL commissioner Sir Peter Hendy told Charles about a steam train that had run on the Tube two weeks ago to mark the anniversary.
"Presumably the whole tunnel gets filled with soot?" Charles asked.
After the journey, Ms Back said: "It was a real honour to sit opposite them - I wasn't quite expecting that.
"She (Camilla) was asking me whether or not I had ever been stuck on one of the trains, when you are led out the front (through the tunnel). Luckily I have not.
"She also asked whether you could walk from one end of the train to the other.
"I spoke about how the new trains have CCTV and are a lot safer.
"She asked whether or not we can get more people on the trains, which obviously we can."
The Prince and Duchess began their day celebrating the Tube by visiting the Crossrail development next to Farringdon station and being shown the area where part of a new station will be built.
The £14.8 billion project will run trains from Maidenhead in Berkshire in the west as far east as Shenfield in Essex, and its central tunnel section should be open by late 2018 with the rest phased in over time.
In pouring rain the Prince and Duchess looked at the Crossrail construction site which was an enormous hole in the ground and met young apprentices who are on an 18-month course learning to spray concrete to make platforms and passenger tunnels.
Later when the royal couple arrived at King's Cross they were taken to the station's Harry Potter attraction - platform 9¾ that the wizard uses to catch a train to Hogwarts School of Witchcraft and Wizardry.
In the JK Rowling books student wizards push their trolleys through a wall to get to the platform and one is now embedded in some brickwork as if it is about to reach the fabled destination.
Fans of the young wizard can pose for a picture with the trolley and Camilla duly obliged while Charles laughed off requests from the waiting media telling his wife "Come away darling, you'll be there all day".
Actor Jim Parkes, 29, from Staines who takes pictures of the public for a Harry Potter shop based at King's Cross, cajoled the Duchess to put her hand on the trolley and laughing she asked him "Do you think I can get through the wall?"
But despite her best efforts she remained in the land of the muggles - non-magicians.
After their visit to King's Cross, Charles and Camilla were driven a couple of hundred yards to the St Pancras Renaissance Hotel to see the results of a £150 million refurbishment of the Midland Railway's original station hotel.
The five-star hotel, which has 245 bedrooms and 38 suites, incorporates Victorian architecture and was part of the original St Pancras Station.
Charles was in his element touring the building, which opened as the Midland Grand Hotel in 1873 before becoming railway offices for 50 years from 1935.
Guests sipping tea or coffee in the lobby got a surprise as the royal couple and their entourage swept into the hotel.
Inside the Booking Office restaurant and bar, Charles and Camilla each tried a cup of a Victorian rum and cognac-based drink called Billy Dawson's Punch. They both knocked them back, looking slightly flushed afterwards.
Camilla, who spent the previous morning standing outside in the rain and mud watching soldiers from 4th Battalion The Rifles at Bulford Camp in Wiltshire, said with a smile on her face: "It's a bit warmer than yesterday."
As surprised guests looked on, she and Charles sat down for a cup of tea with the hotel's co-owners, Harry Handelsman and Lord Fink, as well as general manager Kevin Kelly.
Before they left, they were shown around some of the more ornate parts of the Victorian building, including a spectacular staircase and a sitting room named after the hotel's original designer, Sir George Gilbert Scott, an English Gothic revival architect.
The hotel's refurbishment has been credited with sparking a wider regeneration of the King's Cross and St Pancras area of London.
Lord Fink said Charles appeared to have enjoyed the visit. "He was impressed by the use of the original space," he said.
Handelsman said the royal visit endorsed all the hard work put in during a six-year project to restore the hotel to its former glories.
But he added the building was for everyone. "Often these Grade I-listed buildings are just for the few but here if you are a visitor in London you can come in for a coffee."
Before they left, the royal couple signed the visitors book. "Is it still January?" the Prince asked before laughing. "I've signed the wrong page."
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