I would call this the town's living room.
It was rather hard trying to provide an address for the Jardine as the way I always found it was by looking for the steeple of the Parroquia (big pink church) and walking toward it. You can almost always see the steeple as it is sort of in the middle of town both vertically and horizontally. I'm sure there really is an address for the Jardine but I don't know what it is.
On my worn out little map the Jardine is on either Correo or Umaran on the south side (Correo becomes Umaran, or perhaps Umaran becomes Correo?), and it's on either Canal or San Francisco on the north side (same thing with the streets switching names), on the east is definitely Reloj but on the west could be Cuna de Allende or Hidalgo (switching again). Everyone knows where it is and if you've at least mastered your directions in Spanish it should not be a problem having someone point you there.
The night before the Day of the Dead there were fireworks and bands and people partying in the Jardine into the early morning hours - lots of kids in costume with bags full of candy and coins. It was quite a good time. On most holidays there is something going on around the Jardine.
On non-festive days there is still quite a bit to see - there are trees and pigeon poop covered benches, street vendors, students, cafes, churches, a bank (with ATM), an ice cream shop and a police station all on or facing the Jardine.
You may find yourself spending a portion of every day either sitting in or walking through the Jardine. In the early morning it's full of newspaper readers, in the afternoons with mothers & children, late afternoon is for the older students, and night is for everyone in town. If you're bored you can go to the Jardine and find someone looking for a chat, if you're hating the people with whom you are on vacation you can go the Jardine to escape them, if you want to see who is new in town they're bound to be walking lost around the Jardine, want to run into someone that's lived in San Miguel for years - go to the Jardine.
If you want to be completely alone and wish to neither see nor be seen - don't go to the Jardine, instead go to the Parque Benito Juarez.