Parque Bicentenario is a large ecological park built on the grounds of a former petroleum refinery. The change of use is part of the interest: industrial land has been remade into open lawns, paths, water, and public gardens.
It is more useful as a northwestern Mexico City stop than as a first-time essential. Go if you are nearby, want green space away from Chapultepec, or are interested in the orchid garden and the site's urban-renewal story.