Where is it?

 

Salpa Line extends from Northern coast of Finnish Gulf to Southern shore of Barentz sea along the state Russian border. Fortification installations are concentrated mostly in the southern sector of the Line - from Finnish Gulf to Kivijarve lake (Saima lake system). So, when you cross the Russian border line, you'll cross the Salpa Line.

It is easy to find, you just need to scan road pointers and look for something like Salpa-asema, Museum, Bunkkeri and etc. Good luck...

Kivijarve lake