On a spring morning, eight o'clock or so, sun still low in the pale sky and the traffic on Twentieth Street only beginning to get noisy, the track is a peaceful proving ground. It is Curtis Park's well-maintained central attraction (there also is a great basketball court and a swimming pool). Two banks of stadium seats rise on the track's eastern and western sides, all the better to observe afternoon and nighttime track-and-field competitions among nearby schools and clubs. And above the seats rise the old shade trees that have beautified Allapattah for decades; they enfold the park, shielding but not removing it from its very urban setting just north of the Miami River in the middle of a seamy, down-at-the-heels garment district.