Margaret Pace Park offers a variety of recreation, fitness, and relaxation opportunities. The north end has a basketball court, complemented at the south by two tennis courts and two sand volleyball courts. The rest is mostly free, wide-open grassy space for soccer, football and (at the designated area in the north end) letting your dog run wild. It has a wide concrete pedestrian loop around the perimeter which I estimate at about three-fourths of a mile; eight Vita Course stations suggest calisthenics and other simple exercises. Along the paths, you have several seating areas, plus picnic tables (at least one I know of with a grill). But almost all seating is either concrete or stone, and there's very little shade for most of the day (especially significant from about May through November).
Blocked in by 30+ story condos and a hotel to the west and south, the east shore offers an welcome expansive view across Biscayne Bay to Miami Beach in the distance. Three tall folk-art mosaic "thrones" also adorn that east perimeter path.
The park has two small dedicated areas: (1) a shaded and safely fenced-in children's playground, and (2) an excellent adult workout area with various bars, ramps, and a basic range of machines with no weights. (I'm sure fitness pros have a name for this kind of apparatus; the workout depends on your own speed, intensity, range, and duration of motion.)
Caution for early risers and after-workday visitors: the public rest rooms evidently open at 9:00. At least I've never seen them open before then. I suspect that they close around sunset. Recommended length of visit during those hours? As long as you want. Twenty minutes for a quick lunch, an hour to play with your dog, several hours to lie on the grass and read—enjoy.
Also, if you're driving, allow time to snag a Pay-to-Park space. Parkside spaces along Bayshore Drive tend to fill up quickly; finding one often requires looping the area repeatedly. I usually have better luck finding a space just on the west side of the condos. You'll also find more parking across Biscayne Boulevard, only two blocks away.