Lake Livojarvi is Posio's summer escape: clear water, sandy beaches, and enough space to make the Lapland forest feel unexpectedly beachy. Locals sometimes sell it as "Lapland's Riviera", which is a little grand, but the water and sand are real.
The Hirsiniemi nature trail loops through the lakeshore country and has campfire sites along the way. You will want a car, and the minor roads can be rough.