"Myllykoski" means "mill rapids" in Finnish — the village grew up around the mills that exploited this stretch of the Kymijoki. From the late 19th century the rapids powered a major paper mill, which dominated the town's economy for over a century until its closure in 2011.
What remains is a quieter waterside walk, the former mill buildings (partly repurposed), and a still-running hydroelectric plant. The rapids themselves are now reduced by the dam but worth the short walk from Myllykoski station.