Tom Dixon is known not only for his furniture designs but his transformation of public spaces to celebrate design. On several occasions he's taken over Trafalgar Square in large installation and public events, including -
A) The Bombay Sapphire Stretch of 2005 (80 metres of temporary public seating
B) The Great Chair Grab of 2006 (hundreds of moulded chairs used in the square then given away for free)
C) The Great Light Giveaway of 2007 (Hundred of energy efficient bulbs used in a light installation and then given away for free)
Like these project, you might consider free giveways, the visual impact of repetitive forms, and the idea of scale in your PARK designs.