Mäntyviita separates the two outpost defense lines in Tapiola, still the area is a local outside museum. The nature area hides away man-made structures of defense lines, that has been made in the First World War Period.
Trench are scattered both sides of the road, it's apart of a crescent shaped outpost structure around the Helsinki Metropolitan area, still remarkable sight to visit. In Tapiola there's four outpost areas that has fascinating safe rooms on the area. Make sure that you take consideration of dangers before heading to the sites.
Terrain is really rocky, good shoes are required. Be careful on the site, trenches are some places pretty deep, danger to fall is possible.