Lanark is a modest market town in the upper Clyde Valley, and by itself it would be easy to pass over. Its strength is what lies just below and around it: New Lanark, a preserved 18th-century mill village and UNESCO World Heritage Site, and the Falls of Clyde, where the river drops through wooded ravines.
That combination makes Lanark a real day from Glasgow rather than just another commuter town. Start with the mill village, walk up beside the Clyde to the falls, and leave time for the smaller town sights: the old churchyard, Castlebank Park, the odd rooftop dog on Castlegate, and Thomas Telford's high bridge over Mouse Water.
Lanark also has a place in the William Wallace story. In 1297, Wallace killed the English sheriff here, an act that helped turn local revolt into the First War of Scottish Independence. The town does not overplay the connection, which is wise; the landscape and New Lanark are the real reasons to come.
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