Wikipedia:Picture of the day/November 11, 2004
The London Millennium Footbridge opened on June 10, 2000. Unexpected lateral vibration required the bridge to be closed on June 12 for modifications. The movements were produced by the sheer numbers of pedestrians (90,000 people on the first day, with up to 2,000 on the bridge at any one time). The initial small vibrations encouraged the users to walk in synchronisation with the sway, increasing the effect. This swaying motion earned it the nickname the Wobbly Bridge.