Every summer, the Serpentine Gallery art space in Hyde Park, transforms the space outside the east wing of the permanent building in to an interactive temporary structure, designed by one of the world's leading architects.
This year's design, by Japanese architect Sou Fujimoto, has colloquially become known as The Digital Cloud.
The white latticed structure allows the visitor to walk through, around, and on top of the "cloud", experiencing different viewpoints from within and without.
Every October the pavillion closes and is demolished, in this case perhaps dismantled, and the ground is left to recover for another year, before something beautiful and new goes up in its place.
We don't know what it will be, it's just another of London's secrets.