Ur was an ancient city-state (PROSE: Timewyrm: Genesys [+]John Peel, Virgin New Adventures (Virgin Books, 1991).) in lower Mesopotamia.
In 1924, River Song took a boat to Ur on the way to a Surene tomb in the area. (AUDIO: The Boundless Sea [+]Jenny Colgan, The Diary of River Song: Series One (The Diary of River Song, Big Finish Productions, 2015).)