As reported by the BBC:
A stray dog has completed a 1700km journey across China after joining a cycle race from Sichuan province to Tibet.And he has those short little legs!
The dog, nicknamed "Xiaosa", joined the cyclists after one of them gave him food. He ran with them for 24 days, covering up to 60km a day, and climbing 12 mountains.
Addendum/amendment/clarification: A tip of the hat to Nolandda, who found a report here indicating that while the dog "accompanied" the cyclists on their journey, it did not run the entire distance; they built a cage to carry her on portions of the trip (and in fact some of the cyclists took the bus when the road was too steep).