Here are some glimpses of the madcap event.
Don't look twice! No, you are not seeing wrong. These people are in their underwear on the subway. Talk about a fashion fail! Photograph: Hannibal Hanschke/Reuters
The event began as a madcap idea by a handful of people on New York City's mass transit system in 2002 has grown into an international celebration of silliness. Photograph: David W Cerny/Reuters
The event is held across the world in different countries such as Germany, Czech Republic, the United Kingdom and the USA. Photograph: Hannibal Hanschke/Reuters
Bemused passengers awkwardly averted their gaze as hundreds of commuters stripped down to their underwear for the bizarre annual tradition. Photograph: David W Cerny/Reuters
There are some 9,000-10,000 people who take part each year in the global good-willed stunt. Photograph: Hannibal Hanschke/Reuters
Organisers urged commuters not to wear anything 'overly close fitting' so nobody is upset. Photograph: Hannibal Hanschke/Reuters
The world from the skies is just UNREAL!
Please, don't try this!
OMG! This slide is made of nightmares
OMG! There's a GIANT spider on the loose in France
Would you use this glass toilet?