What do you do when you need to show how London's Super Sewer will rejuvenate the River Thames and make its water less shitty?
You build a botanical garden in it, using recycled rubbish from the Thames itself. Then you run a competition for the London public to win tickets to visit it, 50 metres below London.
Add a soundscape made by the composer of Kew Gardens, some scent technology that replicates the floral aromas of wetlands, and you've got yourself the perfect PR stunt.