This post explores the system, and presents a unique look inside parts of the system few have seen in decades.
"Before developing a deeper appreciation of the system we were drawn initially to the abandoned stations. Some of these seem totally abandoned and haven't been reappropriated for other uses, some have become RATP storage and others, even more rare, were never even open to the public. With time we would conquer them all.
The stations Arsenal and Champ de Mars are the easiest to visit as they can be reached from the topside so they're as good a place to begin as any. While situated at opposite sides of the city these two stations share a similar story. They were closed on the same day, 2nd September 1939, when the metro employees were recruited to join the war effort. After the conclusion of the war they were never reopened for general service as they're simply so close to other stations. The paris metro is one of the most dense in the world with an average distance between stations of ~500m."
Thanks to BLDGBLOG