Make sure you face the green fence with lots of signs and cameras and stop there. To get a different view, you can also walk a bit further past the corner, towards the sign that says number 115 and stop there, but always keep the pedestrian crossings behind you.
Maybe you can’t see it, but you are actually facing a giant body of water. Belgrand's workers finished building this réservoir in 1873, and at that time it was the largest of its kind in the world. There’s no opening on the top, the grass slopes go all the way over the block, to prevent the water from evaporating, and protect it from pollution.
Look up at the strange glass house on the top of the building, and imagine all the pipes coming from all over the countryside to this building. The names of the sources and the year they got connected are written in mosaic on the wall facing you. Below that room is a fake stone grotto --they were big on fake grottos in the 1800s, it showed dominion over nature.
This grotto contained "troutometers". That’s right until 1996 they kept trout in aquariums, each filled with the water from a different source, and when the fish in an aquarium looked a bit sick, they concluded that water was not fit for human consumption. They are now thankfully using slightly more scientific methods.
From there the water flows down below through giant pipes, a bit like the big green one you see outside on the ground, into reservoirs taking up the entire city block. The deepest is “the cathedral of water” a beautiful forest of stone pillars, 7-meter tall stone arches and lagoon blue water. It’s so glorious, I can’t resist, just wait for a second, I’ll take a dip!
Aaah… It is so cold! 12°C is nice but cold! But nice! Well, after all this talk about water, maybe you’re a bit thirsty and frustrated you can’t get to that green fountain in front of you. Let’s walk towards one you can actually use.
OK, so put your back against the green gate in the fence at the very corner of the réservoir. To your right is a café-brasserie, a bit to the left is the tiny playground island where we came from.
We will now cross the street back towards that playground island but will turn left and away from the pirate ship slide. With the pirate ship behind you, walk towards the sound of running water, keeping the réservoir Montsouris to your left.