Anybody done this? I've just 'registered my interest'.

http://www.standuptocancer.org.uk/london3peaks

Looks like an easier alternative to the marathon and the views must be pretty amazing. From the blurb, 'The event combines challenging tower runs up three of London’s tallest buildings, a 5K run between locations, and a terrifying abseil off the third tower as the ultimate finale. Over 350 participants firstly conquered 30 St Mary Axe (The Gherkin), moving to Salesforce Tower London (formerly known as Heron Tower) and finishing at 200 Aldersgate, to take on the 185ft abseil off the 12th floor of the building.'