In the West of Paris, between the Périphérique (ring road) and the business district of La Défense, you can find one of the biggest public parks of Paris: with its 8.46 km², it is more than 3 times bigger than Hyde Park + Kensington Gardens in London or 2.5 times bigger than Central Park in NYC.
This place has several disadvantages: it is difficult to reach via metro; it is crossed by wide avenues with sometimes high traffic; some areas are private (sports or upper society clubs); and it suffers from its reputation of being mostly a prostitution area.
But these inconveniences should not deter you to admire the beautiful landscapes designed around 1850 to provide more greenery to Paris and to offer the upper classes open air distractions. Beyond the typical lakes, cascades, and sinuous lines (that you can find at a smaller scale at Parc Montsouris or the Buttes-Chaumont), it hosts one of the most romantic gardens (Bagatelle and its famous roses), an unusual area in homage to Shakespeare plays, and since 2014 the spectacular architecture of Fondation Louis Vuitton (for contemporary art), designed by worldwide famous architect Frank Gehry, that you can reach with a special €1 shuttle leaving from the Arc de Triomphe (Avenue de Friedland).