Calderwood Linn, also known as Castle Falls or locally as the Big Linn, is a waterfall on the Rotten Calder Water in South Lanarkshire, Scotland.

It sits within the wooded gorge section of the river downstream of East Kilbride, near the site of the old Calderwood Castle.

The fall is one of a long series of named linns along the Rotten Calder, which include Torrance Linn, Black Linn, Trough Linn, and Crossbasket Linn among others.

The surrounding glen is part of a landscape celebrated since the 18th and 19th centuries for its romantic gorge scenery, ivy-clad crags, and woodland.

Calderwood Linn can be reached via an out-and-back walking route through Calderglen Country Park, intermittently waymarked with red castle symbols.