Länsimäki is really a local outside museum. The area has been buried underneath the time itself, the man-made structures of defence lines, that has been made in the First World War. More about history : http://www.rky.fi/read/asp/r_kohde_det.aspx?KOHDE_ID=1570
The Base set: battlefields, intact two-piece safe room, lookout post and machine gun stations, barbed wire remnants, and a old roadway. There are good area maps in the area. Summer destination.
Terrain is really rocky, good shoes are required. Be careful on the site, trenches are some places pretty deep, danger to fall is possible.