Lemmenjoki national park in Lapland is the most northern national park of Finland. I made a canoe trip there a couple years ago down the river Lemmenjoki. Lemmenjoki river valley from Njurkulahti to Kultasatama is one of the most memorable places I have paddled. It is real wilderness though hiking trails follow the shores. It is about 22 km one way.
To Kultasatama you go upstream and in some places you have to pull your canoe from the shore. Even local long boats carrying hikers to Kultasatama go upstream though they unburden their load by letting hikers for a walk while passing streams. You better be prepared with good water shoes.
Along the river there are several tent and fire sites and a few wilderness hut, from these you can find best description on retkikartta.fi. Quite many hikers go to Kultasatama by boats from Njurkulahti and then leave for the paths in wilderness. In July the weather was quite nice, with for some reason no mosquitos but even bigger horseflies.