The Duke of York will abseil down the Shard skyscraper in London for charity today.
Other participants include Ffion Hague, the wife of Foreign Secretary William Hague, and leading businessmen and women.
The Shard is the tallest building in Europe, and its viewing galleries will be open to the public in February next year.
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The outage struck Hartfield-Jackson Atlanta International Airport at around 1pm local time, stopping all outgoing flights.
It will be a chilly day for many parts with the highest temperatures, about 10 Celsius (50F) in the far northwest.
The social site has been overhauling many of its policies in recent weeks following repeated criticism over how it handles abusive content.