Haven’t got a ticket for the tri events? Then fret ye not, for everywhere is free to view apart from the bridge and, obviously, the ticketed venue itself.
But the best vantage points from which to watch the action are: The Wellington Arch (number 1 on the map)/Hyde Park Corner; Buckingham Palace (2, use Green Park tube station); the south side of the Serpentine Bridge (access onto the bridge will not be possible during the event); The Lido (3, one of the best vantage spots for the swim and run); Hercules Monument (4); South Carriage Drive and inside the park at Knightsbridge (southern access from South Kensington and Knightsbridge tube stations).
The BT London Live site (number 5 on the map), as the name suggests, will be showing the triathlon live, free, on a large screen. The area has space for 80,000 people.