Hundreds of commuters in London, Berlin and Prague stripped off their trousers to take a half-naked trip for the annual No Trousers On The Tube ride.
The event is part of the worldwide No Pants Subway Ride, which began in New York in 2002 and has since spread to more than 60 cities across the globe.
In London, crowds met outside the National Gallery in Trafalgar Square before heading underground where they boarded trains on different Tube lines across the capital.
More than 100 people piled on to the Piccadilly Line, where they struggled to remove their trousers due to the large crowds.
Regular Sunday passengers were left bewildered as men and women sat in their brightly-coloured underwear talking, reading and taking pictures of each other.
After changing to the Jubilee Line at Green Park, the group got off at Canary Wharf to do some aerobics on the platform before jumping on another train.
Other groups set off for London landmarks, including one which headed to Parliament.
Sisters Tessa and Matilda Deterding said they had come for the first time because they liked the idea behind it.
Tessa, 24, from London, said: 'We read about it and thought it sounded hilarious. I wasn't nervous about it.
'I quite like the sentiment behind it, instead of a stiff upper lip it's having a bit of a laugh.'
Matilda, 22, said: 'I did especially pick out my pants, you have got to pick out a nice opaque one.
You don't want to give too much of a spectacle.'
Trouserless revellers then headed to The Chandos pub in Trafalger Square for an after party.
The London event was organised by the Stiff Upper Lip Society, which asked participants to 'avoid thongs/budgie-smugglers/anything see-through as we aim to amuse, not offend, fellow Underground users'.
One of the organisers, Farhan Rasheed, said there was not really an aim to the event, it was just a bit of fun.
He added: 'There is no point to it, we are not campaigning or raising awareness of anything.
'People just have fun doing it, it's a bit of a nonsense day out.
'You very rarely get people who are offended. It's London and London is used to this stuff, they take it in their stride and get back to their book.'
The event also took place in Berlin and Prague on Sunday as dozens of passengers hopped on the Metro and U-Bahn half dressed.
Some participants in Germany dressed even more elaborately in bright orange Lycra shirts with their hair sprayed pink.
The No Pants Subway Ride was also reported to have taken place across Chicago, New York City, Amsterdam and San Francisco this weekend.
This article has been adapted from its original source.
© Associated Newspapers Ltd.