My sister used to draw pedestrian maps of the Paris metro, to discover the “One way” paths that you can take upstream (can, but may not!). Sometimes a 100m walk

My sister used to draw pedestrian maps of the Paris metro, to discover the “One way” paths that you can take upstream (can, but may not!). Sometimes a 100m walk can become 5m. Very uncitizenly of her, but very amusing.