Tom Daley was the first person to dive at the 2012 Aquatics Centre - and also got his first look at the gold medal he will be hoping to take home with him.
The dive was part of a series of events to mark the one-year countdown to the games, and the 17-year-old described being chosen to open the £269m centre an "incredible honour".
After the dive, Daley said: "It was great to think that is what it is going to be like next year. It is just incredible. The atmosphere was great with the amount of cheers so it is going to be awesome next year."
The medal, designed by the British artist David Watkins, bears the traditional image of Nike, the Greek Goddess of victory on the front (the same image that has appeared on all Olympic medals).
On the back are five symbols, representing five unique aspects of the London Games.
Crowds and athletes also gathered in Trafalgar Square to see the official countdown clock tick over.