Submitted by thesandpeople100, who says:

Cutaway diagram of the Paris Metro’s Opera station. I came across this working on a project for a hypothetical addition to Palais Garnier but couldn’t find any information on its origin. Any ideas?

Transit Maps says:

A reverse image search on Google found the answer to this pretty quickly: this beautiful cutaway appeared in the July 1910 issue of Popular Mechanics. Unfortunately, this month isn’t available in Google Books’ archive of back issues of the magazine, but there are some good details about the article on this web page (scroll down to get to the cutaway).

The author seemed pretty impressed by what he saw in Paris back in 1910:

Of all the wonderful engineering work done by the Metropolitan underground railways of Paris, the most complicated is that under the Place de l’Opera, where three great tubes cross each other, all of which must have station facilities in the crossing’s tangle. The three tubes, the platform, stairways, and elevators constitute a veritable Chinese puzzle, and the wonder is that the congested underground and overhead traffic has not been even more disturbed during the work.