Montseny is a known nature reserve in Spain.
You go on the freeway of Barcelona in the direction of Girona (that is to the north) , it is on your left.
Of the freeway there is an exit with the same name.

You can read a short description in German language here.

If you once want to examine the area for a walk more nearly, drop in here anyway

Way description:
As one can gather from the green plan, most aims are at the exit Sant Celoni.
One takes this exit, one passes through the village Sant Celoni and then drives according to the signposts.