If you're going to visit Everglades National Park, you should make a point of including Shark Valley on your agenda. It's on the Tamiami Trail at the northern entrance to the park. This area of the park includes a 15-mile loop road that takes you up to a 65' observation tower. From that vantage point, you'll be able to see all of the best features the Glades has to offer. Take in some bird watching. View turtles, birds, and yes, gators.
If you're up for some exercise, you may want to opt for a two-hour bike ride around the loop. Shark Valley also offers two-hour guided tours that are chocked full of educational information. The visitor center itself offers a variety of programs and exhibits.