Blue Peter presenter Helen Skelton is to walk a tightrope between chimneys at Battersea Power Station to raise money for Comic Relief.
The 27-year-old is due to walk the 150m (492ft) long wire at the south London building on 28 February.
She will be at a height of 66m (216ft) and holding a pole in front of her to help balance.
A safety belt will be attached to her in case she falls while walking along the wire.
'Incredibly painful'
The BBC children's presenter said she was inspired to take on the challenge after watching the documentary Man On Wire, which shows Frenchman Philippe Petit walk a tightrope between the twin towers at New York's World Trade Center in 1974.
"I was so impressed when I saw the film that I said 'wouldn't it be amazing to do something like that'," she said.
Skelton has been secretly training in France for the challenge.
"I knew it would be scary and a challenge to stay focused but I really hadn't realised how physical it would be. I am covered in bruises from falling on the wire, which is incredibly painful.
"It has been hard work but that's what is going to make me grit my teeth and keep going when my arms burn.
"I only hope I can hold my nerve and keep my eyes on the wire - if I stay focused I'm sure I can make it across."
Skelton became the first person to solo kayak the Amazon during a challenge for Sport Relief in February 2010.
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