Asked by: David Smith, London
The longest known single journey was that of a Doctor Who postcard in a bottle, thrown into the sea at Tyne and Wear in 2011. This turned up 17 months later in Perth, Western Australia – over 14,500km away. But in 1929, German marine scientists dropped a bottle into the Indian Ocean with instructions for the finder to report where it washed up and then throw it back. This floated for six years and covered 25,600km!