As 95% of Biscayne Nat. Park is water, the best way to appreciate it is to take the boat trip out to Boca Chita Key (provided by the Biscayne National Park Institute). I would recommend booking on the Institute’s website as space on the boat is limited. The cost approx. $40 per person is excellent value.
The BNPI guides give an overview of the park and it’s ecosystems and a potted history of Boca Chita Key. The speedboat ride out to the Key is exhilarating, but be warned if sitting towards the back you could possibly get a soaking!
The lighthouse on BCK is only opened for a short time each day, (by the boat staff) so take advantage & climb up the steps to get a great perspective of the area. Afterwards there is plenty of time to explore the Key before the return journey. All in all we found this was a far superior experience than we had in Everglades NP!
Note the Key is open to private boats so on a weekend there are likely to be plenty of other people about.