An Invisible City Beneath Paris

The plan of the above-ground city is traced carefully in pale silver-gray ink, such that, if you read only for the gray, you can discern the faint footprints of apartment blocks and embassies, parks and ornamental gardens, boulevards and streets, the churches, the railway lines and the train stations, all hovering there, intricate and immaterial. The map’s real content—the topography it inks in black and blue and orange and red—is the invisible city, the realm out of which, over centuries, the upper city has been hewn and drawn, block by block. A subterranean town-planning system was established whereby chambers and tunnels were named in relation to the streets above them, thus creating a mirror city, with the ground serving as the line of symmetry.

Source: www.newyorker.com