Sanquhar /ˈsæŋkər/ (Scots: Sanchar, Scottish Gaelic: Seanchair) is a town on the River Nith in Dumfries and Galloway, Scotland. It lies north of Thornhill and west of Moffat. It is a former Royal Burgh.Sanquhar is notable for its tiny post office (established in 1712), claimed to be the oldest working post office in the world.