So I am from New York - and as a New Yorker, I spent many countless hours walking down the High…read moreLine, which is this park repurposed from the old High Line railroad that did industrial/commercial deliveries from Penn Station down to around Canal Street - that railroad shut down back in the early '80s, and a decent chunk of it was torn down and built into expensive-as-heck luxury condos and whatnot...but that being said, a large chunk remained between Chelsea market and the massive LIRR trainyard next to Penn Station, and during the 2000s it was repurposed as a New York City park. Us New Yorkers, we are arrogant people - we live in the best city in the United States, we are cultured and we are streetwise...until we visit Paris, then we are browbeaten by a city with a 2000+ year history and all the cultural baggage that entails, and of course, they got their high line first, and it's the Promenade Plantee/Viaduc Des Arts.
Just like the story of the high line, the promenade was anchored to a massive train station (the old, historically listed Gare De Bastille), now replaced by the Bastille National Opera house. Part of that line was repurposed into the Southeastern branch of the RER A line. The rest which sits in the city limits between the Opera and the Petit Ceinture (the little belt railway that surrounds Paris right at the border) were abandoned in place until it was repurposed into the Promenade Plantee.
Just like the High Line, there are 3 recognizable segments of the Promenade. The first section is the viaduct that starts from approximately where Rue De Lyon splits from Avenue Daumesnil, to around the area of Gare De Lyon/Rue De Rambouillet - this is where most visitors take their pictures.
At that point, section 2 begins - part of the original viaduct was torn down and replaced by apartment buildings, and you'll be on new, purpose built areas. There is a free public lavatory here, and you'll have a short walk until you see a large park, Jardin de reuilly. You will then be on a bridge crossing into Allee Vinvaldi, a ground-level promenade for a residential area. Just keep your bearings and continue moving forward - you should see a somewhat large overpass ahead of you that has rock structures built into the wall - thus begins part 3.
Part 3 is actually the most fun of the promenade since it has some large well-lit tunnels punching below several important streets in the Pricpus area - you would eventually end up in an area under Station Bel-Air on Line 6, and after a short walk, reach a fork on the walk at Rue De Toul. You can either follow the main-line to Boulevard Peripherique, or take the right fork and head to a park near the junction to the Petit Ceinture - in this case, exit the park on Rottemburg (away from the T3 traimway) and you should reach Michel Bizot/Daumesnil for the Metro Line 8 stop.
Overall, quite a fun walk, around 2-3 miles depending on your endurance, very light elevation changes, and lots to see.