With a few hundred protected acres just outside of Negril, the Royal Palm Reserve is your best bet to see endemic plants and animals in western Jamaica. A boardwalk covers most of the park (and keeps you out of the marsh) and a wooden watchtower gives an excellent view of the palm trees, butterflies, crocodiles, turtles, waterfowl, and more.
Located just off of Sheffield Road, we suggest getting a taxi or driving a rental car, because route taxis won't get you all the way there. Entrance is $10 USD per person for a few hours of hiking and wildlife viewing.
Note:Unless you care to know the names of the species of flora and fauna in the park, it will be cheaper not to take a guided tour.