Visitors will be able to try out five giant slides that have been unveiled at the London gallery. The largest of the spiralling slides is more than 55m (182ft) long and descends from the fifth floor of the venue. Artist Carsten Holler said his work, 'Test Site', was a "playground for the body and the brain". He says slides can help combat mental health problems.The slides are the seventh exhibit in the series commissioned for the gallery's Turbine Hall.