IJ, a double lake in the Netherlands (the digraph IJ is sometimes considered a single letter in Dutch, so this could also be seen as a one-letter name)
Tu, a city in Japan. Tu is in Kunrei-shiki romanization and Tsu in Hepburn romanization is more common. (Other than Mount E this is the shortest place name in Japan in both Japanese phonology and orthography. All other Japanese place names in this section require at least two kana.)