This image shows the bustling activity in front of the Paris Opera House, formally known as the Palais Garner.

The description states:
PARIS… en flanant
7 Place de l’Opera
— This building was constructed between 1861 and 1875, and has become famous from it being used as the centerpiece of the 1910 Gaston Leroux book “The Phantom of the Opera”
This image likely dates from the 1930s.

This image shows the world famous French Gothic cathedral known commonly as Notre Dame, though there are many such churches with this prefix world wide.

The description states:
PARIS… en flanant
4 Notre-Dame
et le Square de l’Arrevêché
–The latter statement translates to ‘the square of the Archbishopric, so described since the cathedral is the seat of the Archbishop of Paris.
On 15 April 2019, workers performing maintenance on the roof of the cathedral ignited a fire that quickly spread out of control among the ‘forest’ of 600 year old timbers, completely consuming the roof and causing the 19th century spire to collapse, piercing the interior ceiling and crashing to the floor of the transept. 
Firefighters were able to extinguish the flames before the rest of the structure was engulfed or compromised, but the ceiling will now need extensive repair and the roof will have to be completely reconstructed.
This image likely dates from the 1930s.

This image shows the iconic Eiffel Tower, located in Paris, France. When originally constructed, it was considered to be an eyesore, presumably because of it’s industrial style construction, but has since become the symbol of Paris more than any other object.

The description states simply:
PARIS… en flanant
10 La Tour Eiffel
–There are elevators to take visitors up to the second level above ground, but beyond that ascending requires climbing a prodigious amount of stairs. At the summit all of central Paris is easily visible on a clear day.
This image likely dates from the 1930s.

This is an image of the famous Arc de Triomphe de l’Etoile, or the Triumphal Arch of the Star, as it stands in the center of a roundabout in the Champs-Élysées.

The description on the back states:
PARIS… EN FLANANT
6   L’Arc de Triomphe de l’Étoile
–The title means Paris…while strolling. The arch was built to commemorate the heroes of the French Revolution and the Napoleonic Wars. One unknown soldier from World War One is buried beneath the arch.
This image likely dates from the 1930s.