You can traverse the rooftop walkway and take in views for up to 15 miles from the observation deck, including Greenwich, the Olympic Park, The Shard and Canary Wharf
The guided climb, which Time Out gives four stars, will take you 52 metres above the city
"An exhilarating ascent" -- Condé Nast Traveller
Weekday climbs are £24.00, and the weekend ones are £29.00. Read the notes before you buy so that you're aware of the T&Cs etc etc.