The 12th : "Green, Spacious, Familial"
Square Trousseau - Marché d'Aligre - Viaduc des Arts - Bercy - Bois de Vincennes
Similar to the 16th, on the opposite side of Paris, the 12th is one of the largest arrondissements, even more so given that the vast Bois de Vincennes is officially a part of it.
As such, any attempt to characterize it in a single stroke would be misguided. Perhaps the best simplification would be to identify three distinct areas within the arrondissement.
The first of these, centered around the Square Trousseau and the Marché d'Aligre, is one of my best-loved neighborhoods in Paris. It can be loosely contained within a triangle, connecting the dots between Bastille, Nation, and Daumesnil. Bordering the 11th, it shares much of the same vibe: dynamic, trendy, and foody. Crossing back and forth across rue du Faubourg Saint-Antoine, you'd have to really pay attention to know whether you're in the 11th or the 12th, and whichever side you live on allows you to enjoy the benefits of the "other side".
This part of the 12th offers a peculiar blend of elegance, authenticity, architectural diversity, convenience, and proximity to green areas such as the Coulée Verte, Parc de Reuilly, Parce de Bercy, Jardin des Plantes, and Bois de Vincennes. The architecture is a fascinating composite of older plastered buildings, elegant Haussmann buildings, and decorative brick & stone edifices from the early 20th century. The Viaduc des Arts (Avenue Daumesnil) is a particularly striking architectural feature, including the surrounding buildings dating mostly from the early 20th century.
The large territory east and south of Place de la Nation, referred to as Bel-Air, is off the map for any ordinary tourist. It is a predominately residential sector with a blend of majestic Haussmannian and more contemporary architecture. There is plenty to take, and plenty to leave. Beautiful free-standing homes line the Bois de Vincennes, offering perhaps the greatest asset of this arrondissement for families, dog walkers, joggers, and cyclists.
In a city that lacks, because of its density, sufficient green space, it is worth mentioning that you can actually enjoy a 9km-long 100% greenbelt experience, starting from Bastille (behind the Opera) walking down the "Coulée Verte" until you reach the Jardin de Reuilly, at which point you continue along the "Promenade Plantée" all the way to the far side of the Bois de Vincennes. For the Paris connaisseurs, there is also a walkable section of the "Petite Ceinture", which is a long-abandoned railway ring around Paris, progressively converted into bohemian parkland with wildflowers pushing their way up against the rusted iron rails.
The remaining part of the 12th follows the Seine from Bastille to the Charenton. A massive amount of space has been historically allocated to the railways and docks. Since much has been renovated over the past thirty years, this part of the 12th doesn't quite feel like the Paris most people know and love. The main features here are the Parc de Bercy and the so-called "Village Saint-Emilion", once warehouses for wine that have since been transformed into boutiques.