My first experience of these gardens dates back to the 1950s, when my family moved from Bologna to Milan. In my memories as a child, a feature that no longer exists remains most impressed: the zoo, located in the north-west corner of the park; a magical place for me, but really too small to ensure animal welfare (and in fact it was definitively closed in 1992). But I remember other salient features very well, such as the scenography of artificial rocks on the north side (towards the Bastions of Porta Venezia) and internal waterways and lakes, with a slow and placid stream, and bordered by huge trees. Of course also the Natural History Museum and the Planetarium; but these are attractions apart.
The position of the garden may seem central today (and it is); but consider that the "Ramparts of Porta Venezia" (on which today a car avenue runs), with which the gardens border to the north, were occupied precisely by the ramparts, so-called "Spanish", because they were built by the viceroy of Spain (ruler of Milan at the time) in the mid-16th century. So the gardens, when they were established (from what I read, in 1784, the time of Austrian domination over the city) were very much on the outskirts.
The architect who designed the gardens was Giuseppe Piermarini, representative of neoclassical art in Italy, known above all for having built the Teatro alla Scala. Instead, the arrangement with false rocks, streams and lakes, referring to the experience of the English "landscape gardens", dates back to 1881, the year in which a memorable exhibition took place, the Italian National Exhibition, occupying part of the garden, which consecrated the role of Milan as the economic capital of Italy.
Overall, the gardens are now a remarkable green lung of the city of Milan, all the more precious because it is central in the city today.