entrance to Gare Montparnasse?

Google is showing you that walking route because you asked for "Montparnasse 2 - Gare TGV", which is not what you want, it's like a different terminal at an airport, although not totally seperated once inside.

If you just asked for "Montparnasse" and let it add 75014 Paris it would have dropped you very close to where Streeview takes over! Follow that and go to Hall 1.

https://www.garemontparnasse.paris/plan-gare-montparnasse.php

I don't know where the "official" entrance to Gare Montparnasse is, but when I took the train to Bayonne last year, I entered at the plaza location (your second hyperlink), and that worked just fine.

When I searched google maps for "montparnasse", I scrolled through the list and chose "montparnasse 2 - gare tgv". In retrospect, the wrong choice. Thanks for the correction. and the link to the gare montparnasse web site.

Ok, it's the entrance at Vaugirard.

Thanks to both of you.

jag

There are multiple entrances to the station. There are entrances from the main square, form the Avenue de Maine and the Boulevard to Vaugirard, as well as from the Metro. There are also other minor entrances.
Then there is the "Place des Martirs" which sits above the tracks at the end opposite from the main terminal. There is access to the platforms from there as well. That is where you end up if you go to "Montparnasse 2 TGV".

As common for big railway stations they are integrated in the urban fabric around them. A significant number of people passing through that station every day aren't even there to take a train...

There is a plan of the station here:

https://www.garemontparnasse.paris/plan-gare-montparnasse.php