The Langinkoski Imperial Fishing Hut is the most famous sightseeing destination along Kymijoki. It was built in the late 19th century at the request of the Tsar of Russia. Today, the fishing hut acts as a museum. The museum is surrounded by a nature reserve.
https://www.kansallismuseo.fi/fi/langinkoski
There are two fine parks along the river, of which the Karhula River Park has won several awards at various park contests. The River Park is also a Green Flag certified park. The Siikakoski Rapids Park, created in 2020, has a network of hiking routes snaking around the nature reserve in addition to the park areas.
The rapids of the Kymijoki downriver as a whole are a must-see sight. You can also explore the rapids along a cycling route that starts from Kotkansaari and circles through all the rapids. The length of the route is 24 km.
One way to enjoy the nature of Kymijoki is to wander along the shores of the river and enjoy the peace and quiet of nature. Everyman’s right is in effect in Finland, allowing free roaming in nature as long as no damages are caused and private property isn’t trespassed on.