The Entrance of Saarijärvi is the park’s northern entrance. It’s usually preferred by mountain bikers and climbers. At the end of Kuismantie you can find the cottage of Savottakämppä which is rentable from Tervarumpu. The area’s guide map, info boards and dry toilets are found at the entrance. There’s also parking for buses.
The address is Kuismantie 985, 52920 Voikoski, Kouvola. Some navigators might offer forest roads as the shortest option, but they are not always drivable. After you reach Voikoski, there are guide signs to Saarijärvi. Drive Mouhuntie towards the Voikoski station (Voikoski as), after a few hundred meters turn left towards Kuisma. Drive until the end of the road, nearly 10km.
Google map: Saarijärvi entrance