Bonn was a city in Germany. The Sixth Doctor visited Bonn in 1770 to attend the birth of Ludwig van Beethoven. (PROSE: Gone Too Soon [+]Christopher M. Wadley, Short Trips and Side Steps (Short Trips short stories, 2000).)
It was the capital of West Germany in 1989. (AUDIO: Protect and Survive [+]Error: Code 2 - no data stored in variables, cache or SMW.)