Rachan Mill, 5 miles (8 km) southeast of Biggar, in the Scottish Borders, is a small group of houses on the junction of the A701 from Edinburgh to Dumfries, and the B712, which runs northeast beside the River Tweed past Drumelzier and Stobo. As the name suggests, Rachan Mill originally grew up around a corn mill, powered by the Holms Water, which runs through the settlement, to join the River Tweed. To the southeast, is the beautiful Rachan Hill and to the northwest, Whitslade Hill.
Rachan House, a well-known Georgian mansion, much altered in Victorian times, once stood northeast of the settlement, on the road to Drumelzier, but was demolished in 1965.
A large block of local whinstone in one the gardens of the settlement, about 1.1m (3½ feet) in size, known as the Piper's Stone, has several legends attached to it, all variants on the theme of Bertram the Cobbler who is said to have played the pipes so well when the king passed by, that he was granted land.