Varkaus is an industrial town in Finnish Lakeland, built around waterways, paper mills, and the narrow passages between lakes. It is not one of Finland's pretty wooden towns, and that is part of the point: Varkaus has a working, slightly odd character of its own.
The best stop is the Museum of Mechanical Music, a wonderfully specific collection of self-playing instruments, jukeboxes, and gramophones. Add the old Taipale Canal, the inhabited Varkaus Water Tower, and the church fresco, and the town clears the bar for a spare day in the region.
Varkaus also sits on the Saimaa waterway, so it works best for travelers already between Kuopio, Savonlinna, and Joensuu. If you want pure lake scenery, keep moving; if you like small industrial towns with one strange museum and real local texture, stop.