If you have a couple of hour free at Montparnasse, why not go for a stroll?
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Strolls
Eiffel Tower and Napoleon (5K green)
If you have a couple of hours spare, why not visit some iconic sites?
Take the exit from the station to Boulevard Vaugirard turn left when you leave the station
Turn right at Boulevard Pasteur and as you walk down it, you should get your first sight of the Eiffel Tower. After around 600m you will see a wide grassy boulevard branching off you your right. Let's walk down that.
This is the Av. de Breteuil which leads all the way to Les Invalides - formerly a hospital for wounded soldiers and now a museum with a Napoleon's tomb.
While here, you could also pop over to the Rodin Museum on the right.
When you have seen enough, lets' go see the Eiffel Tower. Follow the road to the left (Avenue de Tourville). You will know you are going the right way as you should see it.
As the Ave de Tourville peters out, follow the road to the left (Place Joffre) which has the École Militaire on the left. On your right is Grand Palais Éphémère which does a pretty good job of blocking views of the Eiffel Tower. Take one of the paths to the side of it to get to the Champs de Mars which leads to the Eiffel Tower. When you have finished here, continue along the Place Joffre and turn left onto Avenue Sufferin which leads briefly on to Boulevard Garibaldi which has the overhead railway running along it. Continue on to Boulevard Pasteur which will bring you back to Boulevard Vaugirard on your left and the entrance to Montparnasse.
Montparnasse Cemetery (2.5k blue)
Montparnasse Cemetery is the final resting place for around 35,000 souls including some of Frances most famous citizens and is only a short walk from the station. You can pick up a cemetery map at one of the entrances or download it here.
Exit station by the main entrance facing the platforms and on your right is a busy road (Avenue du Maine).
Cross the road at the traffic lights and turn left then take the next right on to Boulevard Edgar Quinet. You will walk along here until you reach the Cemetery on your right, the but the streets that you pass on your right, such as the Rue de la Gaité contain lots of bars and restaurants where you can get revive yourself after your cemetery tour.
Paris Catacombs - from Montparnasse Cemetery (1k black)
It's just a short walk from Montparnasse Cemetery to the Paris Catacombs which were created in the 1780s and modelled on those in Rome. You will need to book a tour in advance. A guided tour around the 1.5k of tunnels will take about an hour.
Exit the Cemetery at the far end from where you entered (Rue Froidevaux) and turn left. The Catacombs are 400m down this road.
Our Lady of Labour (1.5k orange)
A detour on the way back from the Cemetery will take you to a Notre Dame du Travail (Our lady of Labour), which was built for the workers of the 14th Arrondissement. It reused some of the steel framework from the Paris Exhibition and could easily be mistaken for a factory - just what workers wanted to see on their day off... It also houses some arts and crafts paintwork and depictions of the grafters' patron saints.
Exit the Cemetery at the far end from where you entered (Rue Froidevaux) and turn right. At the end of the road take the slight left along Rue Jean Zav and continue along the road until you reach Place de Catalogne. Continue across the Place and through the passageway between two columns. The church is in front of you.
George Brassens (3K red)
This one is perhaps a niche interest, but gives a little insight into French culture. Singer/songwriter George Brassens was a big hit in the post war years. Even for decades after his death, you can still find kids playing his tunes, as I did in Saint-Jean-Pied-de-Port. George came from Sète but spent most of his life in Paris and you can visit his old stomping ground and the park that is now named after him.
The humble place where George started out.
No running water except in the gutter...
The bar where he spend many happy hours with his friends and now has a bit of a shrine to him.
Where he moved to once he sold some records
Where he came to compose his songs - now called Parc George Brassens
Not sure he ever went on this.