Although a bit north of proper downtown, it is a 10 minute walk and a must see, regardless of season. It is on Bull St, which divides east from west, and at the northern top marking the end of the downtown squares. Of course, like the entire city, it is most spectacular in its blooming glory around April.
If timed right, you can catch a free concert on the green, listening to jazz, classical, or other music concerts, with a picnic basket and a bottle of wine.
Don’t forget your camera; many cameo spots.